Gunther

At the very beginning of his career until 2014, Hahn went by the stage name Big Van Walter. The name was a direct reference to Big Van Vader, but it was not a homage. According to Hahn, commentator Mark Landauer gave him the name, and Landauer went on to tell promoters that Hahn's stage name would be Big Van Walter, which annoyed Hahn. Hahn had his first recorded wrestling match on 19 November 2005 in Bern, Switzerland, competing in a tag team match alongside SigMasta Rappo (who, at the time, was under the ring-name Sigi The SwissTank); they lost to the High Class Catch Club (Baron von Hagen and Adam Polak). At the time of this match, Walter was 18 years old. He had his first singles match on 25 March 2006 in Bad Vöslau, defeating Sigi The SwissTank. In the early months of his career, he had his first matches with future rivals and wXw colleagues John Klinger and Absolute Andy, as well as competing in matches with the likes of Colt Cabana, Pac and "Bambikiller" Chris Raaber.

According to Hahn, he wanted to initially hone his skills and train further in the United States; however, Chris Raaber wanted him to train in Japan due to the similarities within one of Raaber's trainers, Dory Funk Jr., and current puroresu trainers. Raaber reached out to Pro Wrestling ZERO1-MAX, the founded promotion of Shinya Hashimoto and Shinjiro Otani, and asked if Hahn could train with ZERO1-MAX and its heavyweight trainers, which consisted of Riki Choshu and his mentor Tomohiro Ishii, and Tatsuhito Takaiwa. Hahn began training at the ZERO1-MAX dojo, which had also been a training facility used by members of the HUSTLE and Pride Fighting Championship rosters, in December 2006. Hahn was assigned the gimmick of Gha-cha-ping, the off-shoot wrestling gimmick of Hirake! Ponkikki [jp] character Gachapin. For the gimmick, Hahn had his hair dyed green and wore a mask to the ring, complete with a light green singlet with yellow and pink lines in the center, contrasting to Gachapin.

He made his debut as Gha-cha-ping on 17 January 2007, teaming with Raaber (as Bambikiller) to defeat Otani and Rikiya Fudo. For two days afterwards, Hahn defeated Fudo in singles matches and then Fuyujirou Jidosha [jp]. His first loss as the gimmick came on 10 February, losing to Kohei Sato in Hiroshima; he lost to him again in Nagano on 19 February as well. His last match on the tour took place on 7 April, defeating Jidosha, as Jiro Kuruma, at the Yasukuni Shrine Sumo Wrestling Place in Tokyo.

Hahn returned to Japan in 2008, ditching the Gha-cha-ping gimmick and going as Big Van Walter, for two shows for the Makehen promotion. First, on 19 March, he teamed with Lance Archer, who went by his real name Lance Hoyt, losing to Masato Shibata (the future Mad Paulie) and Tomohiko Hashimoto. On 28 March, he teamed with Daisuke Sekimoto to defeat Shibata and Hashimoto.

In the midst of his run in wXw, in 2011, he took part in numerous shows with their main Japanese partner at the time, Big Japan Pro Wrestling. At Korakuen Hall, on 28 April, he defeated then-rookie Ryuichi Kawakami. Four days later, on 2 May, he defeated Daisuke Sekimoto to win the wXw Unified World Wrestling Championship, his second reign overall. In Yokohama, on 5 May, he teamed with Combat Zone Wrestling (CZW) owner D. J. Hyde to defeat Abdullah Kobayashi and Shadow WX. He returned to Japan in April 2012, teaming with Sekimoto to defeat Yoshihito Sasaki and BJW Strong ace Yuji Okabayashi. On 5 May 2012, Walter was defeated by Sasaki in a match to crown the inaugural BJW World Strong Heavyweight champion in Yokohama, a defeat considered vengeful for Sasaki as Walter had defeated him in a Unified World Wrestling Championship defense a year prior. Two months later, in July 2007, he took part in an inter-promotional tour with BJW, wXw and CZW wrestlers on a "World Triangle Night" showcase tour. The first match of the tour for Walter, on 27 July, involved him and fellow wXw wrestlers Robert Dreissker and "Bad Bones" John Klinger losing to Okabayashi, Sekimoto and Sasaki. Walter and Dreissker, who would later be known as the AUTsiders in Europe, defeated Sasaki and Shinya Ishikawa a day later. On 29 July, he and Klinger defeated Okabayashi and Sekimoto, and then defeated Okabayashi in a singles match hours later. On 30 July, he and Dreissker failed to win the wXw World Tag Team Championships, losing to the Sumerian Death Squad (Tommy End and Michael Dante).

In late 2019, it was announced that Walter would compete at BJW's Ryogokutan 2019 show, at the Ryōgoku Kokugikan, where he would team with Sekimoto to face Okabayashi and Yuji Hino. Sekimoto and Walter won the match, and it was acclaimed positively.

Immediately following his tour in ZERO1-MAX, Walter made his Westside Xtreme Wrestling (wXw) debut on 4 May 2007 as Big Van Walter, in a match that also involved Atsushi Aoki, Adam Polak, and Tengkwa on the pre-show of that year's 16 Carat Gold Tournament. Within his first full year in the company, he faced numerous wrestlers in high profile singles and tag team matches; some of his opponents included former GHC Heavyweight Champion Takeshi Rikio, Roderick Strong, Low Ki, Drake Younger (Wuertz), Pierre Carl Ouellet, and Steve Douglas. On 22 June 2008, Walter had a high profile tag team match at wXw and Pro Wrestling NOAH's Dead End VIII: European Navigation series, where, in Oberhausen, he and John Klinger lost to future NOAH ace Go Shiozaki and Kenta Kobashi. Kobashi would be an inspiration to Walter and his wrestling style in the years following their encounter, particularly with Walter's usage of the Burning Sword chop strike.

In 2009, Walter would align himself with trainer Tatsuhito Takaiwa, Sha Samuels, Terry Frazier and Sami Callihan to form The Catch Hoolz. Their first matches as an official unit were at the 16 Carat Gold shows that March. During the shows, Walter competed in the 16 Carat Gold tournament, defeating Erick Stevens before losing to Drake Younger between 6 and 7 March. The Catch Hoolz were later joined by Jon Ryan in September that year. Walter would have his first matches for a wXw championship on 3 October 2009, where he would have two chances at the wXw World Tag Team Championship. First, he would face the reigning champions and Catch Hoolz colleagues The Kartel (Sha Samuels and Terry Frazier) alongside Callihan as Walter's partner in a semi-final contest in a tag title tournament. During the match, Walter turned on Callihan, kicked him out of The Catch Hoolz, and became absent from the match; in the process, Walter became established as a top heel in the company. Subsequently added was Callihan's Switchblade Conspiracy partner, Jon Moxley, and they would defeat The Kartel to win the titles minutes later. At the main event of the show, Walter would align himself with D. J. Hyde to face both The Kartel and the Switchblade Conspiracy, as well as the other semi-final team of Axeman Axel Tischer and Bernd Föhr, in a four-way elimination match, which Walter lost after Hyde was pinned at the end of the match by the Switchblade Conspiracy. At the end of the year's 9th Anniversary show, he defeated Doug Williams.

2010 proved to be the biggest year of Walter's wXw career at that time. In March 2010, Walter competed at that year's 16 Carat Gold tournament, where he defeated Daisuke Sekimoto, Munenori Sawa, Erick Stevens, and ultimately Chris Hero to win the tournament for the first and only time. At 23 years old, he became the youngest winner of the tournament at the time. At the time of him winning the tournament, the wXw World Heavyweight Champion was Steve Douglas, however, he would not challenge for the title as it was discontinued to make way for the Unified World Wrestling Championship, which was won in its inaugural match in June that year by Zack Sabre Jr., who was the wXw World Lightweight Champion at the time of the unification. Walter faced Zack Sabre Jr. in what would be the latter's first defense of the new championship, with Walter defeating Sabre via disqualification. Within this time, Walter began to form an alliance with the Sumerian Death Squad (Tommy End and Michael Dante), and subsequently competed alongside them in matches under the name "The Mind". After a tag team match opposing both wrestlers ended in a no contest in September 2010 (which also involved the inclusion and firing of Karsten Beck from The Mind and the inclusion of Adam Polak, the "mastermind" of the group), Walter was announced to be part of a championship rematch at "HATEs Fuckin' Birthday Show" on 2 October 2010 in Oberhausen. After hitting Sabre. with his trademark powerbomb, Walter defeated him to become wXw Unified World Wrestling Champion. 5 days later at a CZW cross-promotional event, he defeated 2Face in his first defense. On 4 December at wXw's 10th Anniversary show, he retained against Ares.

Walter lost the Unified World Wrestling Championship to Daisuke Sekimoto on 15 January 2011 in Oberhausen. In March, he competed in that year's 16 Carat Gold tournament, where he defeated Rico Bushido, Go Shiozaki and Mark Haskins in first round, quarter-final and semi-final matches, before losing to Callihan in the finals. He won the Unified World Wrestling Championship back on 2 May, during a Big Japan Pro Wrestling card in Tokyo's Shin-Kiba 1st Ring. He would defeat Shuhei Taniguchi in his first defense, before defeating Zack Sabre Jr. at the "With You, Japan!" event. Within that time, Karsten Beck was accepted into the stable, and The Mind officially became a quintet. At Broken Rulz XI, he successfully defended the Unified World Wrestling Championship against Axeman Axel Tischer. On the first day of the Nordrhein-Westfalen Triangle Of Ultraviolence: Messengers Of Death weekend shows in October with wXw, BJW and CZW, The Mind was aligned with Adam Cole and Drew Gulak to compete in a four-on-four tag team match alongside Walter and Beck; they defeated 2Face, Chuck Taylor, Marty Scurll and Sami Callihan in the match and, the next day, Walter defended the Unified World Wrestling Championship successfully against Yoshihito Sasaki. On 26 November, The Mind was officially disbanded after Adam Polak announced he'd step away from professional wrestling. In events before his title loss, he would successfully defend against Scurll, Jon Ryan, Shinya Ishikawa and Sekimoto.

El Generico won the 2012 16 Carat Gold tournament by defeating Tommy End in the final. At Dead End XII on 19 May 2012, Generico faced Walter for the Unified World Wrestling Title, defeating Walter and ending his reign at 383 days (the second longest reign at the time in the overall lineage behind Ares' second World Heavyweight Championship reign).

At 16 Carat Gold 2012, Walter started a partnership with fellow Austrian wrestler Robert Dreissker, being dubbed "The AUTsiders" later on. Walter and Dreissker defeated Jay Skillet and Jonathan Gresham to win the wXw World Tag Team Championship at day three of 16 Carat Gold on 3 March 2013, a day after Walter failed to win his third Unified World Wrestling Championship against Axel Tischer. Their first defense of the titles came at the Hasta La Victoria Siempre Tour Finale, where they would defeat the Sumerian Death Squad and the Leaders Of The New School (Zack Sabre Jr. and Marty Scurll). During the reign they would successfully defend against the teams of Masashi Takeda and Drake Younger, Skillet and Ricky Marvin, D. J. Hyde and Karsten Beck (two allies of the tag team), and Maxi Schneider and Michael Schenkenberg. They would later lose the titles at 258 days in Hamburg during the 13th Anniversary tour to Hot & Spicy (Axel Dieter Jr. and Da Mack).

In October 2013, Walter competed at a ceremonial World Triangle League tournament with CZW and BJW wrestlers. He was one of three wXw qualifying wrestlers (alongside Dreiskker and John Klinger). Walter lost his block by losing to eventual overall winner Daisuke Sekimoto on the third day of the tournament after defeating Drake Younger and Kim Ray on the first and second days respectively.

Walter lost a top contendership match to the Unified World Wrestling Championship against Zack Sabre Jr. at Back To The Roots XIII on 18 January 2014. Starting at 16 Carat Gold 2014, he went by the ring name Big Daddy Walter. After defeating Sasa Keel (who initially won by disqualification) and Johnny Gargano during the tournament, he lost by disqualification to Axel Tischer in the semi-finals after Walter was blamed by the referee for a hit with the Unified World Wrestling Championship on Tischer, which was executed by the then-champion Tommy End, and after numerous assault attempts made by Tischer and the Keel Holding stable. Although Tischer lost the tournament after losing to Chris Hero, Walter began to blame End and the Keel Holding stable for his downfall in the tournament. Walter defeated Tischer in a 16 Carat Gold rematch on 29 March. On 5 April, Walter failed to win the wXw Shotgun Championship against Axel Tischer in a match that also involved Chris Rush and Drake Younger. He lost in the finals of the Mitteldeutschland Cup that year to Axel Dieter Jr., in a match that also involved Da Mack and Karsten Beck. During the evolving rivalry with the Sumerian Death Squad and Keel Holding, Walter won the annual Shortcut To The Top battle royale on 31 May. On 27 July, Walter defeated Tommy End to win his third Unified World Wrestling Championship.

His first successful defense was two months later on 20 September, defeating Sasa Keel. At the World Triangle League series that year, Walter defended against Tommy End in a two-out-of-three-falls match, where End gained the first fall in nine seconds after striking Walter with a knee strike and a double foot stomp from the top rope, and Walter subsequently defeated End two falls in a row with a powerbomb and a lariat respectively. After the end of the match, End made peace with Walter, shaking his hand. During the 14th Anniversary tour, he defeated Absolute Andy, Axel Dieter Jr., and Chris Hero in title defenses. At the finale of the tour, he, along with Dreissker, Mike Schwarz and Chris Masters defeated Keel Holding in an four-on-four "relaxed rules" match.

Upon winning a 30-minute street fight alongside Dreissker and Prost (Mike Schwarz and Toby Blunt) at Back At The Roots XIV, Vince Russo made a surprise appearance and announced he had been the new investor of wXw. Russo brought out Karsten Beck still in his ring gear after his match earlier in the show, and Beck challenged Walter to an impromptu championship match. Beck defeated Walter after Russo screwed over Walter by attacking the referee and Sha Samuels assaulted Walter whilst the referee was downed. Russo took off his jacket to reveal a referee shirt and did the three count to declare Beck the champion. Later on, Walter failed to win both the Tag Team and Unified World Wrestling titles, defeating Lucas Di Leo and Peter Fischer by disqualification and losing to Beck yet again during the 2015 16 Carat Gold weekend after his AUTsiders team mate, Robert Dreissker, hit Walter with a cowbell to cost him the championship whilst former The Mind stablemate Adam Polak distracted him in a surprise return to the company. Amidst his ongoing rivalries within wXw, Walter began to ally himself with the likes of Yoshihiro Takayama, Hot & Spicy, Sean Waltman, John Klinger and more to combat Beck and his allies (predominantly the Reich Und Schön tag team consisting of Kevin Roadster and Marius von Beethoven) and Polak and Driessker's Cerberus stable. Yet again, Walter lost to Beck for the title at Broken Rulz XV.

During the ongoing feuds, Walter began to have a close partnership with Zack Sabre Jr. and Hot & Spicy. At the 2015 World Tag Team Tournament, Walter was paired with Sabre. The tournament would be for the vacated World Tag Team Championships. After defeating Karl Anderson and Doc Gallows of Bullet Club, Reich Und Schön, and the Calamari Catch Kings (Chris Brookes and Jonathan Gresham) in the earlier stages, the duo defeated reDRagon to win the titles.

On 7 November in Prague, Czechia, Walter took part in a special contest involving Nigel McGuinness being the special guest referee. He would win the match with Czech wrestler Atom, defeating Jurn Simmons and Karsten Beck. The Big Daddy Walter name was discontinued in July 2016; there on, Walter began to use the all caps mononym WALTER.

In 2015, Walter, alongside Axel Dieter Jr., Axel Tischer and Christian Michael Jakobi, the then-head booker and managing director of wXw, released an apparel brand entitled Ringkampf (German: ring fight). Its apparel became worn by all three members (except Jakobi) throughout 2015 and 2016. In 2016, however, Ringkampf evolved into a full-on stable. For months, Walter appeared to have an alliance with American wrestler Timothy Thatcher, who shared a similar style to Walter. After Dieter, Walter and Thatcher began appearing aligned with each other in August of that year in the lead up to the World Tag Team League that'd happen between 31 October and 2 November, the three, along with Jakobi, created the Ringkampf stable and began sharing its motto, "Die Matte Ist Hellig" (German: "The Mat is Sacred"). The philosophy of Ringkampf was that they would only care about the scarcity of professional wrestling and the stable's superiority over all. Walter began to incorporate the nickname "The Ring General" within this time period. Thatcher and Walter were allied together to compete at the World Tag Team League; they defeated Moustache Mountain and Los Güeros del Cielo on the first and third days of the weekend, and lost to JML (David Starr and Shane Strickland) on the second day, failing to reach the finals. Nevertheless, the team of Walter and Dieter were granted a wXw World Tag Team Championship match at the 16th Anniversary show on 10 December, against the incumbent champions, A4 (Absolute Andy and Marius Al-Ani), in a two-out-of-three falls match, which they lost two falls to one.

At a show in London on 28 January 2017, Walter lost a top contendership match to Jurn Simmons. Afterwards, Ringkampf started a series of matches with A4, who had been rivalrous to Ringkampf since the latter's World Tag Team League run. Between 11 and 24 February, Ringkampf and A4, who also competed alongside Simmons and Günter Schmid, had their overall match series tied 2-2, notably after Ringkampf's Dieter and Walter beat A4 at Dead End XVI. At a show in Düsseldorf on 4 March, Walter lost to Matt Riddle. Walter later competed at the 2017 16 Carat Gold tournament, along with the coinciding AMBITION 8 between 10 to 12 March. After beating David Starr and Marius Al-Ani by referee's decision within two days, Walter vengefully defeated Matt Riddle before losing to Ilja Dragunov in the finals of the tournament. At the AMBITION 8 tournament, he lost in the first round to Jeff Cobb.

Within 31 March and 6 June 2017, Walter failed to gain the Unified World Wrestling Championship thrice by losing to the incumbent champion, Jurn Simmons. First, on 31 March, he lost to him by pinfall in a singles match in Ludwigshafen, then lost in a four-way match that also involved Axel Dieter Jr. and Mike Bailey on 8 April in Dresden, and finally during another singles match in Erfurt. It was announced in April 2017 that Axel Dieter Jr. would leave wXw to sign with WWE. He failed to win the Shortcut To The Top battle royale on 1 July. At Inner Circle 4 on 5 October 2017, amidst the World Tag Team League weekend, he defeated Thatcher in an "AMBITION rules" match. At the same time, they were partnered up in the league itself. They advanced in their block, defeated The Briscoe Brothers and EYFBO in the process, whilst losing to Homicide and Low Ki, They defeated David Starr and Jurn Simmons in the finals of the tournament, and, in the process, also won the wXw World Tag Team Championships, his third overall reign.

On 15 October 2017, in Leipzig, Walter failed to win the Unified World Wrestling Championship again, this time in a no contest in a four-way match against incumbent champion John Klinger (who had become the biggest heel in the company with his faction RISE), Ilja Dragunov and Jurn Simmons. Thatcher and Walter's first defense as World Tag Team Champions came on 3 November, defeating Bobby Gunns and Jaxon Stone. The next day, on 4 November, they successfully defended against RISE members Da Mack and leader John Klinger. They defeated them again, successfully defending the titles, on 17 November, whilst defeating Stone and Gunns again the next day in a tornado-tag elimination match. They defeated Julian Nero and Dreissker on 8 December, with Dreissker now going by the name Avalanche. On 23 December, at wXw's 17 Anniversary, Walter and Thatcher defeated Tarkan Aslan and his brother Lucky Kid in another successful defense.

At the 16 Carat Gold 2018 weekend, Walter was scheduled to compete in a wXw Unified World Wrestling Championship match at the Saturday show against John Klinger. However, Walter announced before the beginning of the match that the stipulation had changed to a three-way and, subsequently, Ilja Dragunov returned to the company to face both Klinger and Walter. Dragunov defeated both to win the championship, after striking Klinger with his Torpedo Moskau maneuver. The next day, Thatcher and Walter lost their tag titles to Klinger and Da Mack.

Between 24 March and 5 May, Walter failed to, yet again, win the Unified World Wrestling Championship. Dragunov would defeat Walter, alongside David Starr and Travis Banks, at a show in London on 24 March, and then defeat Walter in 3 straight championship matches on 13 April, 14 April and 5 May in Limbach-Oberfrohna, Dresden and Oberhausen respectively. He failed to win both the Shortcut To The Top battle royale and the World Tag Team Championships in August and September, and failed to win the World Tag Team League in October with Thatcher, despite their two wins in their four-team block. He failed to win the Shotgun Championship against Marius Al-Ani in Hof in October 2018. Walter did, in contrast to his shortcomings, win the AMBITION 11 tournament on 8 August 2019 in Toronto, Ontario, Canada.

During the 2019 16 Carat Gold tournament between 8 and 10 March 2019, Walter lost in the finals to Lucky Kid after he defeated David Starr, Fenix and Avalanche in the previous stages. At Superstars of Wrestling on 1 June, after Walter defeated Wheeler Yuta earlier in the show, Walter and Ilja attacked Aussie Open and "Hardcore" Bob Holly after their match on the show. During the assault, Walter and Ilja attacked the wXw fans and stated that the "hard work [they] put in ... is the only reason wXw is able to have people in attendance". At the Shortcup To The Top 2019 event on 3 August, he and Ilja Dragunov defeated Aussie Open to win the World Tag Team Championships, with Walter now being a four-time tag champion. On 3 August, Walter failed to win the Shortcut To The Top battle royale again, this time losing to Timothy Thatcher. On 9 August in Toronto, Walter defeated Daisuke Sekimoto. On 13 September, Walter and Dragunov lost their titles to Aussie Open; they lost in their rematch clause the next day.

Due to him now being signed with WWE and performing on the NXT UK brand, his schedule became slim for independent bookings. Before the start of the COVID-19 pandemic and its spread in Germany, Walter competed on two wXw shows on 8 March during the 16 Carat Gold weekend, first defeating Shigehiro Irie on a live stream and, later, at the 16 Carat show itself, Thatcher and Walter collaborated with Daisuke Ikeda and Yuki Ishikawa, with Walter and Ikeda losing to Thatcher and Ishikawa in a tag team match. Walter had his final wXw match to date on 18 December 2021, defeating Cara Noir at their 21st Anniversary show.

On 20 November 2015 at a Tetsujin show in Liverpool, Walter defeated Tommy End. On 23 March 2018, he competed as a surprise opponent for Flash Morgan Webster and his ATTACK! Championship at the "ATTACK! Festival Of Power" show in Cheltenham, losing to Webster and failing to win the championship. He competed at the Pro Wrestling Chaos event "CHAO5" on 9 June, losing to Big Grizzly for the promotion's King Of Chaos Championship. On 5 July, he made his TNT Extreme Wrestling debut, losing to Joseph Conners for the TNT World Championship; he later competed again for the title on 6 September in a triple threat with him and Conners losing to Jordan Devlin for the title.

On 4 May in Brighton and Hove, Walter competed at Riptide Wrestling's Spring Break event, where he would win against Wild Boar in a qualifier for the Riptide Brighton Championship tournament. He returned to Riptide on 6 July at "International Waters", defeating Mike Bailey. At the first day of the tournament weekend on 2 August, he lost to Jonah Rock in a first round contest. The next day, he and Timothy Thatcher defeated Aussie Open.

Walter, as Big Van Walter, made his wrestling debut in the United Kingdom between 24 and 25 September 2011, competing at Wolverhampton-based promotion Fight Club: PRO's Project Mayhem weekend shows. On both days, he successfully defeated Dave Mastiff and Trent Seven, first he defeated both in a tag team match alongside Dan Ryder, and later defeated both in a three-way match for Walter's Unified World Wrestling Championship. Walter returned to Fight Club: PRO on 23 February 2018 at "A Tribute To Francois Trebec", where he defeated David Starr.

On 29 June 2018, at the "International Tekkers: Nothing Is True, Everything Is Permitted" event, he, alongside Chris Brookes and Kid Lykos of CCK, defeated Mark Davis, Jimmy Havoc and Travis Banks. Within this time period, Walter would become a part of the stable Schadenfreude, of which Brookes was the leader of; as such, he would be part of the top heel unit in the entirety of FCP. He defeated Omari for the Infinity Cup at the "Big Strong Bois" event on 27 July. During the Project Mayhem VII weekend between 27 and 28 August 2018, he, Aussie Open and Chris Brookes lost to Moustache Mountain, Omari and Meiko Satomura by disqualification, and defeated #STRONGHEARTS members CIMA and T-Hawk alongside Davis. At the "Infinity 2018" event on 26 October, he, Brookes and Timothy Thatcher defeated The Hunter Brothers and Omari. He and Thatcher lost to The Hunter Brothers at the next show, "FCP 100", on 30 November. The next day, at the Schedenfreude-produced event "WELTSCHMERZ", he defeated Masato Tanaka.

On 1 February 2019, he lost to Mark Davis via a piledriver, which was considered an upset; after the match, Thatcher called off their fellow Schadenfreude members from a presumed attack, but Thatcher attacked Walter with a rear naked choke during a celebratory pose, which resulted in the rest of the unit attacking Walter and putting him through a table. Walter would return to FCP on 23 August at their "Rise Against" event, where he and Brookes fought to a no contest after Schadenfreude and opposing Fight Club: PRO roster members rushed to the ring. This would be Walter's last match for FCP.

On 13 October 2012, Big Van Walter made his Revolution Pro Wrestling debut in Sittingbourne, Kent, defeating Stixx. The next day, he defeated El Generico. At the Christmas Cracker event on 2 December, he defeated Michael Elgin. Three-and-a-half years later, on 12 June 2016, Walter made his return to the promotion, this time competing as Big Daddy Walter, losing to Big Damo after Walter passed out to Damo's Cú Chulainn's Wrath submission. At a live show in Southampton, he defeated Chris Brookes. In Milton Keynes on 30 June, he defeated Yuji Nagata and, a day later, in Manchester, Yujiro Takahashi, during the Strong Style Evolved UK tour. At Summer Sizzler 2018 on 17 August, he had his one and only wrestling match against one of his trainers, Tomohiro Ishii, for the top contendership to the Undisputed British Heavyweight Championship, losing to Ishii. Walter compted in two tag team matches alongside Ringkampf teammate Timothy Thatcher at the British J Cup weekend on 8 and 9 September 2018, first losing to CCK's Chris Brookes and Jonathan Gresham, and later defeating EYFBO, who had now been affiliated with the Impact Wrestling stable LAX. During the NJPW-RevPro collaborative Global Wars show, he and Thatcher lost to EVIL and SANADA of Los Ingobernables de Japon. At Uprising 2018, he lost to Satoshi Kojima and, in his final RevPro match since, he and Thatcher lost to Aussie Open.

On 24 May 2015, Walter made his Progress Wrestling at the 2015 Super Strong Style 16 Tournament at the Electric Ballroom in London, losing to Rampage Brown in the first round. He competed the next day after being eliminated from the tournament, losing a five-way match to Eddie Dennis that also involed Damo O'Connor, Jack Gallagher and Zack Gibson. Rampage and Walter met again later in 2015 at Chapter 23: What A Time To Be Alive! in a match notable for the ring breaking after Brown was whipped into the corner. He entered the Super Strong Style 16 Tournament again in 2016, reaching the quarter-finals before being eliminated by Chris Hero. Walter participated in the tournament to determine the inaugural Progress Atlas champion in 2016 but he finished the tournament with 2 points.

At Chapter 42 on 15 January 2017, Ringkampf made their Progress debut, defeating The London Riots. In the lead-up to their match with the South Pacific Power Trip (TK Cooper and Travis Banks), Ringkampf declared that they "despised" The London Riots and they are to "save the sport of professional wrestling". They were defeated by the South Pacific Power Trip in the match on 29 January. On 26 March, Walter lost to Matt Riddle in an Atlas Championship challenge. At Chapter 47, Ringkampf challenged British Strong Style (Pete Dunne, Trent Seven and Tyler Bate) for all of their championships, in a six-man tag team match, unsuccessfully challenging all of them. He defeated Matt Riddle to win the Atlas Championship at Chapter 51: Screaming For Progress at the O2 Academy Birmingham. He lost the title to Riddle a little over a month later on a Progress card in New York City after defending it against Fred Yehi a day prior, but recaptured it at Chapter 55: Chase The Sun at Alexandra Palace in a three-way match that also involved Matt Riddle and Timothy Thatcher. Within his reign, he successfully defended the title against ICW wrestler Wolfgang, Rampage Brown and Timothy Thatcher and failed to win the Tag Team titles against CCK's Chris Brookes and Kid Lykos.

At Chapter 68: Super Strong Style 16 Tournament Edition 2018, Walter vacated the Atlas title in order to chase the Progress World title, held by Travis Banks. After defeating Zack Sabre Jr. in a top contendership match, he failed to win the championship by count-out on the second day of the Super Strong Style 16 weekend; however, at Chapter 74: Mid Week Matters, he defeated Banks to win the title. His four defenses of the championship took place in the United States between 9 and 12 August: he first defeat Jimmy Havoc and Schaff in Seattle at two separate shows (one was held by Defy Wrestling), in Chicago he defeated Eddie Dennis, and finally in Livonia, Michigan, he defeated Mark Andrews. At Progress' "Hello Wembley!" event, he competed against top contender Tyler Bate in a thirty-minute match, defeating him after he connected Bate with a Fire Thunder driver. At the next Progress show a month later, he defeated Zack Sabre Jr. in a title defense. After Walter successfully defended later on against Mark Haskins, Shigehiro Irie and Chris Ridgeway at the next few shows, he was challenged by Trent Seven, the then-Atlas Division Champion, to a title unification match. On 5 May 2019, Walter defeated Seven by referee's decision, unifying the belts and winning the Atlas Division Championship for a third time.

At Chapter 91: Prog On The Tyne on 6 July 2019, he defeated Eddie Kingston and, the next day, Ilja Dragunov, in title defenses. At Progress Toronto, he defended successfully against Paul Robinson. At Chapter 95: Still Chasing on 15 September, Walter lost the Progress Unified World Championship when Eddie Dennis successfully cashed in his title opportunity gained by defeating Mark Andrews at Chapter 76. This was a triple threat match also involving David Starr. Afterwards, Walter only had one more Progress match, defeating More Than Hype alongside the Anti-Fun Police on 23 February 2020 at Chapter 103: Beer Snake City.

On 2 June 2018, Walter made his debut for Over The Top Wrestling in Ireland, teaming with Low Ki to defeat OTT ace Jordan Devlin and rival David Starr. At OTT's next event, "That Ring Really Tied The Room Together", on 7 July, he defeated Sean Guinness. During the match, Walter legitimately bruised Guinness on his neck, causing Devlin to console Guinness backstage. This led to a match being scheduled to the OTT World Championship on 18 August for OTT's second annual WrestleRama event, where Walter would be the next challenger to Devlin in a match billed "David vs. Goliath". Similar to that of his win against Tyler Bate, Walter defeated Devlin for the title after he connected with a Fire Thunder driver, to the shock of the crowd. Walter and Timothy Thatcher celebrated in the ring before being confronted by Starr. At OTT's 4th Anniversary show on 13 October, he defeated Will Ospreay with a diving splash. Thatcher and Walter defeated Starr and Devlin at the "Redemption" show on 10 November, and defeated Bonesaw at a show in Belfast on 16 December. On 3 February 2019, Walter and Thatcher failed to win the OTT Tag Team titles against Bonesaw and his partner from "The Kings of The North", Damien Corvin. At their Homecoming 2 event, Pac defeated Walter by disqualification after shoving the referee. Infamously, during the match, Pac dislocated his finger twice after initially landing on it awkwardly after a pinfall attempt. At ScrapperMania 5, on 16 March 2019, Devlin regained the OTT World Championship from Walter. His last match to date for OTT took place on 23 June 2019 for that year's WrestleRama, where he defeated David Starr after locking Starr in a hadaka-jime; he initially lost the match due to disqualification after Starr faked a hit from Walter with WWE United Kingdom Championship belt, but the match was restarted after the referee was notified about the fake hit from Jordan Devlin. The win against Starr meant that Walter had won 27 straight singles matches against him.

It was announced that Walter was making his Defiant Wrestling debut, and was going to be added to the Defiant Internet Championship match of David Starr against Travis Banks at Lights Out on 19 March; however, Banks did not compete due to a foot injury. Instead, Walter would later defeat Starr twice to become the #1 Contender for Banks' title which occurred at Lights Out and a "Road To No Regrets" show on 26 March in a match that had a no rope breaks stipulation. His match with Banks would end in a draw at the No Regrets show on 28 April; he also failed to win the No Regrets Rumble match that same night. On 2 June, Walter defeated Banks and Zack Sabre Jr. to win the Internet Championship. He made his first successful defense of the title at a co-sponsored SMASH Wrestling and Combat Zone Wrestling show on 15 July in Toronto, defeating Matt Cross. On 30 June, an international dream match was scheduled to occur on 26 August at Defiant's "Stacked" show in Manchester, where Walter would defend the Internet Championship against Will Ospreay who, at the time, was signed to New Japan Pro Wrestling. In an acclaimed 22-and-a-half minute match, Walter defeated Ospreay. The match would be given four-and-a-half stars by Dave Meltzer of Wrestling Observer Newsletter. On 11 October at "Fight Or Flight", he defeated Davis in a successful defense. On 30 December 2018, Walter lost the title to Martin Kirby after previously defeating Chris Ridgeway and El Phantasmo in a triple threat match. This was Walter's last appearance for Defiant Wrestling, as WhatCulture would proclaim Defiant defunct in August 2019.

Walter made his debut in North America on 13 March 2010 in Philadelphia, Pennsylvania at two events: Combat Zone Wrestling's "Walking On Pins And Needles" event, where he and Karsten Beck lost to the Crimson City Saga (Tommy End and Zack Sabre Jr.), and wXw's "The Vision", where he defeated Eddie Kingston. He later returned to compete at three shows between 8 and 10 April: first he defeated Devon Moore at the Force One vs. wXw event in Egg Harbor Township, New Jersey, then he and Brodie Lee lost to Johnny Moss and Michael Elgin at the first day of wXw's Kreuzzug weekend, and finally he and Drake Younger defeated Bad Bones and Necro Butcher the next day.

He lost to Donovan Dijak at Beyond Wrestling's "Bye Bye Beautiful" event in Somerville, Massachusetts on 13 August 2017, the same day as a Progress Tag Team title challenge against Moustache Mountain. He competed at All Pro Wrestling's Bay Area Bash event on 22 June 2018, teaming with Timothy Thatcher and losing to Reno SCUM. At "DEFYance United" on 10 August, he defended the Progress World title successfully against Schaff. At REVOLVER Wrestling's "Tales From The Ring 2", he defeated PCO. The next day, at Premiere Wrestling Xperience's "Monsters Among Us" event, he unsuccessfully challenged for the PWX Heavyweight title in a four-way against Elijah Evans IV, in a match that also involved David Starr and John Skyler.

During WrestleMania 34 weekend, Walter competed in numerous matches for Game Changer Wrestling. He defeated "Filthy" Tom Lawlor at Matt Riddle's Bloodsport and lost to PCO at Joey Janela's Spring Break 2.

Walter competed in 16 matches for World Wrestling Network affiliate EVOLVE. He debuted at EVOLVE 90 on 11 August 2017 in Joppa, Maryland, defending the Progress Atlas Championship against Fred Yehi. Walter unsuccessfully challenged for the WWN Championship the next night at EVOLVE 91 in New York City in a four-way match that also involved eventual winner Matt Riddle, Keith Lee, and "Hot Sauce" Tracy Williams. He again made an unsuccessful challenge for the WWN Championship on 9 December 2017 when he was defeated by Lee at EVOLVE 96 in New York City. The next day, at EVOLVE 97, he defeated Matt Riddle. At EVOLVE 98 and 99 on 13 and 14 January 2018, Walter and Timothy Thatcher defeated Catch Point members Dominic Garrini and Tracy Williams, and Walter defeated Zack Sabre Jr. with a Tiger Bomb. At EVOLVE 102 on 5 April during the WrestleMania 34 weekend shows, he and Thatcher defeated Daisuke Sekimoto and Battlarts legend Munenori Sawa in Kenner, Louisiana; the next day, he and Thatcher unsuccessfully challenged for the EVOLVE Tag Team Championships against Chris Dickinson and Jaka. Darby Allin defeated Walter at EVOLVE 106 on 23 June, and, the next day, Walter and Adam Cole held an after-stream dark NXT North American Championship match, which Cole won. In his final matches for EVOLVE between 11 August 2018 and 7 December 2019, he defeated JD Drake twice, Anthony Henry, Chris Hero (who had now wrestled in WWE under the name Kassius Ohno), Timothy Thatcher and Josh Briggs.

Walter made his highly-anticipated Pro Wrestling Guerrilla (PWG) debut by entering the 2017 Battle of Los Angeles tournament, where he was eliminated by eventual finalist Keith Lee in the opening round. During the tournament weekend, he competed in the traditional third-night multi-man tag team match, where he, Brian Cage, Jonah Rock, Sami Callihan and Trevor Lee lost to Chuck Taylor, Flamita, Joey Janela, Mark Haskins and "Flash" Morgan Webster. He was then defeated by Ricochet at the first night of All Star Weekend 13. The next day, he got his first PWG victory by defeating Zack Sabre Jr. in a match that was awarded a five-star rating by Dave Meltzer in the Wrestling Observer Newsletter. At Mystery Vortex V, Walter unsuccessfully challenged for the PWG World Tag Team Championship with Timothy Thatcher, losing to the defending Chosen Bros (Jeff Cobb and Matt Riddle). Between 20 and 21 April 2018, he competed at PWG's All Star Weekend 14. On the first night, he and Thatcher defeated Brody King and Tyler Bateman of Violence Unlimited, then, on the second night, Walter defeated champion Keith Lee and Jonah Rock in a three-way match to win the PWG World Championship. He would successfully defend the championship at Bask In His Glory, the final PWG event at American Legion Post #308 in Reseda, California, against Sammy Guevara. At Threemendous V, he defended against Brody King. Amidst his reign as PWG World Champion, Walter competed in his second Battle of Los Angeles tournament between 14 and 16 September 2018. On the first day, he and Thatcher defeated Ilja Dragunov and Shingo Takagi in a special tag team match; on the second day, each of the teams faced off in first round tournament matches, with Walter defeating Thatcher and Takagi defeating Dragunov. After Walter defeated Jonah Rock the next night, he was eliminated in the semi-finals by Takagi. Walter later lost the PWG World Championship to the eventual BOLA winner, Jeff Cobb, on 19 October at "Smokey And The Bandido", which was also Walter's final PWG match.

On 12 January 2019 at NXT UK TakeOver: Blackpool, Walter made his surprise WWE debut for the NXT UK brand by confronting WWE United Kingdom Champion Pete Dunne after a successful title defense. After striking Dunne's opponent, Joe Coffey, with a big boot, Walter walked out of the ring to the crowd chanting his name and, during his entrance, his theme song: the fourth movement of Dvořák's ninth symphony. The following week, Walter confronted Dunne and Joe Coffey, making his intentions clear for Dunne's championship in the later while. On the 30 January 2019 episode of NXT UK, Walter made his WWE in-ring debut against Jack Starz. He beat Starz in under four minutes. He later defeated Mark Coffey and Kassius Ohno on separate singles matches on the NXT UK programme. He later teamed with Pete Dunne to defeat both Joe and Mark Coffey. On 20 March, Dunne challenged Walter to a championship defense, which was confirmed and signed a week later. At NXT TakeOver: New York on 5 April, Walter defeated Dunne to win the WWE United Kingdom Championship, ending Dunne's record-setting reign at 685 days.

On the 22 May episode of NXT UK, Walter retained the United Kingdom Championship against Dunne in a rematch, after interference by the European Union (Fabian Aichner and Dieter Jr., who had now gone by his real name Marcel Barthel), thus establishing himself as a heel and reuniting Ringkampf under the new name Imperium. The faction would later be joined by Axel Tischer, who had known been signed under the name Alexander Wolfe, after he interfered in a match pitting Imperium against British Strong Style. On the 26 June episode of NXT UK, Walter retained his title against Travis Banks. On 3 July episode, Imperium interfered in Moustache Mountain's title match against Grizzled Young Veterans, therefore making Grizzled Young Veterans retain their titles. After the match, they injured Tyler Bate. On 31 August at NXT UK TakeOver: Cardiff, Walter retained his title against Tyler Bate.

In the build-up for the NXT UK and NXT co-branded event, Worlds Collide, Imperium began feuding with The Undisputed Era (NXT Champion Adam Cole, Roderick Strong, and NXT Tag Team Champions Bobby Fish and Kyle O'Reilly), which was further intensified during the closing moments of NXT UK TakeOver: Blackpool II on 12 January 2020, when the group attacked Imperium following Walter's successful title defense against Joe Coffey. During his reign the following week, the WWE United Kingdom Championship was renamed to NXT United Kingdom Championship and he was presented with a slightly updated belt design, which replaced the WWE logo at the center with the NXT UK logo. On the 29 October episode of NXT UK, Walter retained the championship in a match against Ilja Dragunov in another highly acclaimed match. On 19 February 2021, Walter became the longest-reigning NXT United Kingdom Champion, breaking Pete Dunne's record of 685 days. On the 17 March episode of NXT, Walter would return to the NXT brand and attacked Tommaso Ciampa. On 5 April, his championship reign surpassed the two-year mark. Two days later at Stand & Deliver, Walter retained his title against Ciampa. The next day at NXT UK Prelude, Walter successfully defended his title against Rampage Brown. At NXT TakeOver 36, Walter dropped the title to Dragunov in a rematch after Dragunov secured a standing rear naked choke (hadaka-jime), ending his reign at 870 days. This would be the longest reign in WWE history since 1988 until Roman Reigns surpassed this number with the WWE Universal Championship in January 2023.

At the New Year's Evil special episode of NXT on 4 January 2022, Walter teamed up with Imperium stablemates Fabian Aichner and Marcel Barthel to face Riddle and MSK (Nash Carter and Wes Lee) in a six-man tag team match, which they lost. After having his final match on NXT UK on 13 January where he defeated Nathan Frazer, Walter was transferred to the NXT brand. On the 18 January episode of NXT, Walter defeated Roderick Strong in the main event, after which, he announced his new ring name as Gunther. Controversially, his new name was supposed to be Gunther Stark, however the name was dropped due to its name being linked to a Nazi air force member of the same name. In mid-March, Gunther started a brief feud with LA Knight when he took offense at the latter getting an NXT Championship match by calling out Dolph Ziggler. The next week, after Gunther defeated Duke Hudson, Knight challenged him to a match at NXT Stand & Deliver, which Gunther won. On the 5 April episode of NXT, he faced NXT Champion Bron Breakker in a losing effort, which turned out to be his final appearance for the brand. The loss to Breakker would be the last time Gunther had lost a singles match in WWE until Chad Gable in 2023, and the last time he would be pinned in a singles match until Sami Zayn at Wrestlemania 40 in April 2024.

On the 8 April episode of SmackDown, Gunther and Barthel (now known as Ludwig Kaiser) made their main roster debut, where Gunther defeated Joe Alonzo in a squash match. On the 27 May episode of SmackDown, Gunther and Kaiser made their debut as a tag team, defeating Drew Gulak and Intercontinental Champion Ricochet. On the 10 June episode of SmackDown, Gunther defeated Ricochet to win the Intercontinental Championship, making him the first Austrian to win the title. He would successfully defend the title against Ricochet in a rematch and Shinsuke Nakamura. Prior to Gunther's title defense at Clash at the Castle on 3 September, Ludwig Kaiser announced the reformation of Imperium by reintroducing Fabian Aichner, now known as Giovanni Vinci. Gunther subsequently defeated Sheamus to retain the title in a critically acclaimed match, with many deeming it the best match of the event. Dave Meltzer of the Wrestling Observer Newsletter rated the match five stars, marking Gunther's fifth match to receive five stars, and his first main roster match to receive this rating. He would beat Sheamus in a rematch on the 7 October episode of SmackDown. Gunther spent the remainder of 2022 and the early months of 2023 retaining the Intercontinental Championship against Rey Mysterio, Ricochet, Braun Strowman, and Madcap Moss in respective singles matches on various Smackdown episodes.

At the Royal Rumble on 28 January, Gunther was the first entrant and the last person eliminated from the titular match; he was eliminated by the match's winner Cody Rhodes, who entered as the thirtieth and final participant. His 71 minute and 25 second performance was the longest in the history of the annually-held event. On 9 February, Gunther reached 245 days as champion, surpassing Shelton Benjamin's reign of 244 days, becoming the longest-reigning Intercontinental Champion in the 21st century. On 17 February, Gunther reached 281 days as Intercontinental Champion, surpassing WWE Hall of Famer Mr. Perfect's reign of 280 days, giving him the longest reign as Intercontinental Champion in 34 years. On Night 2 of WrestleMania 39 on 2 April, Gunther retained the title against Sheamus and Drew McIntyre in a critically acclaimed triple threat match. Before Gunther and Imperium moved to Raw, he successfully retained the Intercontinental Championship against Xavier Woods on 21 April edition of Smackdown.

As part of the 2023 WWE Draft, Gunther, along with his Imperium stablemates Ludwig Kaiser and Giovanni Vinci, was drafted to the Raw brand. In the coming months, Gunther successfully defended the Intercontinental Championship against Mustafa Ali at Night of Champions on 27 May, Matt Riddle at Money In The Bank on 1 July, and Drew McIntyre at SummerSlam on 5 August. On the 21 August episode of Raw, Gunther defended the title against Chad Gable but lost the match by countout, ending his undefeated singles streak on the main roster; however, as championships do not change hands by countout or disqualification unless otherwise stipulated, Gunther remained champion. After defeating Gable in a rematch on the 4 September episode of Raw, Gunther guaranteed that he would become the longest-reigning Intercontinental Champion later that week, which he did, breaking The Honky Tonk Man's record of 454 days, which he celebrated on 11 September. Gunther went on to retain his title against Tommaso Ciampa on the 2 October episode of Raw, and Bronson Reed on the 16 October episode of Raw. On 25 November at Survivor Series: WarGames, Gunther successfully defended the Intercontinental Championship against The Miz. The next night on the 27 November episode of Raw, after earning the respect of Gunther, Miz asked for a rematch for the title. Gunther went on to defeat Miz in their rematch on the 18 December episode of Raw, which was under the stipulation that should Miz lose, he can no longer compete for the Intercontinental Championship as long as Gunther is the champion.

On 27 January at Royal Rumble, Gunther entered the Royal Rumble match at number 18, eliminating Jey Uso, Kofi Kingston and The Miz before being eliminated by the winner, Cody Rhodes. The following Raw, Gunther successfully defended the Intercontinental Championship against Kofi Kingston. Gunther defeated Jey Uso on the 19 February episode of Raw to retain his title after interference from Jimmy Uso. On 20 February, Gunther's Intercontinental Championship reign set another record for the title, this time for most cumulative days as champion, surpassing Pedro Morales, who held the title for 619 days across two reigns. Morales had held this record for 41 years. At Night 1 of WrestleMania XL, Gunther was defeated by Sami Zayn for the Intercontinental Championship, ending his historic reign at 666 days and making it his first pinfall loss as part of the main roster.

Gunther made his first WWE appearance since WrestleMania XL on the 22 April episode of Raw, when he announced he would partake in the King of the Ring tournament. On the same episode, Vinci (who'd later be drafted to SmackDown) was kicked out of Imperium by Kaiser, who had assaulted him after their scheduled match; afterward, Kaiser was fined. At the aftermath of the next week's Raw show, Gunther accepted Kaiser kicking out Vinci. After Kaiser and Gunther were kept on Raw during the 2024 WWE Draft, it was announced that Gunther would face off against a returning Sheamus in the first round of the King of the Ring tournament. On the 7 May episode of Raw, Gunther defeated Sheamus in what Sheamus deemed the last match between them. The next week, he defeated Kofi Kingston in a quarterfinal bout, then defeated Jey Uso in the semifinals on 20 May, and finally Randy Orton in the finals at the King and Queen of the Ring event, albeit controversially, after Orton had a shoulder up during the match's ending crucifix pinfall, to win the tournament, earning a World Heavyweight Championship match at SummerSlam.