William, Will, Willie, Bill, Billie, or Billy Thomas may refer to:
Arts
- Billie Thomas (1931–1980), American actor
- Bill Thomas (actor) (born 1952), English actor
- Bill Thomas (author) (1934–2009), American author and photojournalist
- Bill Thomas (costume designer) (1921–2000), American costume designer
- William C. Thomas (1903–1984), American film producer
- William Thomas (actor), Welsh actor
- William Thomas (architect) (1799–1860), Anglo-Canadian architect
- William Thomas (Gwilym Marles) (1834–1879), Welsh poet
- William Thomas (Islwyn) (1832–1878), Welsh poet
- William Thomas, Jr. (born 1947), American actor
- William Tutin Thomas (1829–1892), Anglo-Canadian architect
- Willie Thomas (trumpeter) (born 1931), American jazz trumpeter and educator
- Will Thomas (novelist) (born 1958), American novelist
- Billy Thomas (born 1953), drummer with McBride & the Ride
Politics
US politicians
- Bill Thomas (born 1941), U.S. Representative from California
- Bill Thomas (Alaska politician) (born 1947), member of the Alaska House of Representatives
- Bill Thomas (Montana politician) (born 1935), Democratic Party member of the Montana House of Representatives
- Bill Thomas (writer) (born 1943), American writer
- William D. Thomas (1880–1936), American politician
- William H. Thomas (Waukesha Co.) (1821–1898), American politician
- William Henry Thomas (1920–2009), American politician
- William L. Thomas (born 1967), American judge, nominated to a federal judgeship
- William Kernahan Thomas (1911–2001), American judge
- William Reuben Thomas (1866–1943), American civic leader
- W. C. E. Thomas (William C. E. Thomas, 1818–1876), American civic leader
- William W. Thomas, Jr. (1839–1927), American politician
- W. Aubrey Thomas (1866–1951), U.S. Representative from Ohio
UK politicians
- William Thomas (scholar) (died 1554), MP for Old Sarum and Downton
- William Thomas (MP died 1586), MP for Caernarvonshire
- Sir William Thomas, 1st Baronet (1641–1706), English politician
- Sir William Thomas, 2nd Baronet (died 1777), British politician
- Sir William Thomas, 4th Baronet (1777–1850), British politician
- Sir William Thomas, 5th Baronet (1807–1867), British politician
- William Stanley Russell Thomas (1896–1957), British politician
- William Thomas (MP for Carnarvon) (died 1653), Welsh politician
- William Thomas (MP for Ludgershall) (1630–1686), English lawyer and politician
Other politicians
- William Thomas (Newfoundland politician) (1785–1863), Newfoundland politician
- William Thomas (Australian settler) (1793–1867), Australian colonist
- William Thomas (Australian politician) (1869–1924), Victorian politician
- William Lemen Thomas (1872–1921), Western Australian politician
- Bill Thomas (Australian politician) (born 1950), Western Australian politician
Science
- W. I. Thomas (1863–1947), American sociologist
- William H. Thomas (physician) (born 1959), American physician
Military
- William Holland Thomas (1805–1893), Cherokee chief and American Civil War officer
- William Bain Thomas (1898–1967), British Army officer
- William H. Thomas (Medal of Honor) (1923–1945), American soldier
- William Waffle Thomas (1919–2014), American Air Force officer, former Air Force One pilot
Sports
- Bill Thomas (died 2009), American racecar designer and performance tuner best known for the Bill Thomas Cheetah
- Bill Thomas (American football) (born 1949), American football player
- Bill Thomas (baseball) (1877–1950), American baseball player
- Bill Thomas (ice hockey) (born 1983), American ice hockey player
- Bill Thomas (New Zealand footballer), New Zealand footballer
- Bill Thomas (Australian footballer) (1886–1974), Australian rules footballer
- Bill Thomas (sailor) (born 1925), Canadian former sailor
- Billy Thomas (Australian footballer) (1902–1968), Australian rules footballer
- Billy Thomas (basketball) (born 1975), American basketball player
- Billy Thomas (footballer) (1903–1992), Welsh footballer
- William A. Thomas (born 1948), American football player and coach
- William "Digger" Thomas (1890–1953), Australian rules footballer
- William Lewis Thomas (1913–1995), English rugby footballer
- William Llewellyn Thomas (1872–1943), Welsh rugby union footballer
- William Thomas (cricketer, born 1960), English cricketer
- William Thomas (footballer, born 1885) (1885–?), English soccer player
- William Thomas (karateka), English karateka
- William Thomas (linebacker) (born 1968), American football player
- William Thomas (rugby league born c. 1885) (c. 1885–?), Welsh rugby league footballer
- William Thomas (rugby league born c. 1905) (c. 1905–?), Welsh rugby league footballer
- Willie Thomas (1866–1921), Welsh rugby union footballer
- Will Thomas (basketball) (born 1986), American basketball player
- Tra Thomas (William Thomas, III, born 1974), former American football offensive tackle
- Bill Thomas (footballer, born 1930) (born 1930), Australian footballer
Others
- William ap Thomas (died 1445), Welsh soldier and sheriff
- William Bevil Thomas (1757–1825), Newfoundland merchant and land developer
- William Davies Thomas (1889–1954), Welsh academic
- William Griffith Thomas (1861–1924), English clergyman
- William Luson Thomas (1830–1900), English wood engraver and newspaper founder
- William Fitz Thomas (fl. 15th century), Irish judge
- "William Thomas", an alias of Wilhelm Thomas, who gained notoriety in the Adolph Beck case
- William Thomas (bishop) (1613–1689), bishop of Worcester
- William S. Thomas (died 1986), suffragan bishop of the Episcopal Diocese of Pittsburgh
- William Thomas (Chancellor of Llandaff Cathedral) (1734–1799), Welsh priest and scholar
- William Thomas (Archdeacon of Northumberland) (born 1927), English priest
- William Thomas (activist) (1947–2009), American anti-nuclear activist
- William F. Thomas (1924–2014), American newspaper editor
- William Jenkyn Thomas (1870–1959), Welsh author
- William Kyffin Thomas (1821–1878), newspaper proprietor in South Australia
- William Moy Thomas (1828–1910), English journalist
- Bill Thomas (priest) (born 1943), Archdeacon of Llandaff
- William Beach Thomas (1868–1957), British author and journalist
- William Hannibal Thomas (1843–1935), American teacher, journalist, judge, writer and legislator
- William Thelwall Thomas (1865–1927), Welsh surgeon
- C. William Thomas, American accountant
- William Winstead Thomas (1848–1904), American insurance company president and architect