John Komnenos (Greek: Ἰωάννης Κομνηνός) was a Byzantine aristocrat, the nephew of Emperor Alexios I Komnenos (r. 1081–1118) and long-time governor (doux) of the strategically important city and theme of Dyrrhachium.
John was born probably circa 1074, the eldest son of Alexios's elder brother, the sebastokrator Isaac Komnenos, and his Georgian wife, Irene "of Alania". In 1081, his uncle, Emperor Alexios I Komnenos, proposed a marriage match between John and a German princess to the Holy Roman Emperor Henry IV (r. 1056–1105), but nothing came of this.
In early 1091, John was chosen by Alexios to replace John Doukas as the governor (doux) of Dyrrhachium, in modern-day Albania. The city was of great importance to the Byzantine Empire, as the "key of Albania" and the main point of entry from Italy into the Balkans, a fact illustrated by the role it played in the Norman invasion in the early years of Alexios's reign. Soon after the assumption of his duties, however, he was accused by Theophylact of Bulgaria of plotting against the Byzantine emperor. To defend himself against the accusation, John travelled to Philippopolis, where Alexios resided. It is not clear whether the allegations had any substance; nevertheless, the affair evolved into a family quarrel between Alexios and his brother Isaac, who was also present. Eventually, Alexios dismissed the allegations and reconfirmed John in his post.
Later, in 1094, despite his military inexperience, John was charged with confronting raids by the Serbs under Vukan of Rascia into the Byzantine province. John allowed himself to become involved in prolonged negotiations with the Serbian ruler, giving him valuable time to prepare his forces. When he was ready, Vukan attacked the Byzantines near Lipenion and inflicted a heavy defeat upon them. John travelled to Constantinople to explain his defeat to Alexios, but was not relieved of his post. In 1096, he received and hosted Count Hugh I of Vermandois, whose fleet had shipwrecked off the coast of Dyrrhachium. John was probably still doux of Dyrrhachium in 1105/06, when he is recorded by Anna Komnene to have been defeated in a campaign against the Dalmatians. As the threat of a renewed Norman invasion by Bohemond loomed, the emperor replaced John with his younger brother Alexios.
The name and identity of John's wife is unclear. He may be the nephew of Alexios I Komnenos, who had a nephew named John recorded as marrying an unnamed daughter of Michael VII Doukas (other candidates include John Taronites and Alexios's brother Adrianos Komnenos, who took the monastic name John). Another "John Komnenos", married to an "Anna Doukaina", and their descendants, are mentioned in tomb inscriptions in the Pammakaristos Church in Constantinople, which they founded. Several authors, however, including Paul Magdalino, Jean-Claude Cheynet, and Konstantinos Varzos, identify this John with Adrianos, and not with the governor of Dyrrhachium. The Oxford Dictionary of Byzantium, following these authors, gives the name of John's wife as Maria Doukaina.