Born in 1126 as the oldest child of the
Andronikos Komnenos and his wife Irene, John was orphaned in 1142 when his father died. John came under the protection of his uncle, Emperor
Manuel I Komnenos (), to whom he remained close throughout his life: in his opulent palatial residence in
Constantinople, John commissioned mosaics depicting the martial deeds of the emperors of the
Komnenian dynasty, with an inscription that lauded Manuel as his "spiritual father" and even a "second God". In his youth he was lauded for his beauty, his pale complexion and blond hair. John is first mentioned on campaign in 1146, against the
Sultanate of Rum. In 1148 John took part in a Western-style tournament in
Heraclea, where he was wounded and lost an eye to the lance strike of an Italian knight. As a recompense, Emperor Manuel I gave him the high rank of and appointed him to the office of . This provoked the envy and enmity of the future
Andronikos I Komnenos. This rivalry deepened in the following years, as Andronikos became the lover of John's younger sister, Eudokia, and as a result of a public quarrel in 1154; in the same year, John accused his cousin of intending to assassinate Emperor Manuel, while Andronikos openly proclaimed that he wanted to "cut the head of my biggest enemy", meaning John. This statement led Emperor Manuel to imprison Andronikos. John fought in the
Byzantine–Hungarian wars in 1150, winning a victory against a Hungarian detachment near the
Strymon river. It may be during this campaign that he received a wound to the thigh, and lost the little finger of his left hand. In 1151, John was (military governor) of Sardica (modern
Sofia,
Bulgaria), was of Naissus (modern
Nish, Serbia) , and then governor of
Cyprus in 1155. In the spring of 1156, Cyprus was attacked by
Raynald of Châtillon and
Thoros II of Armenia. While John, with a part of the Byzantine garrison remained at the capital,
Nicosia, the general Michael Branas led a force to confront the invaders. Branas was driven back towards Nicosia, and John led a sally to rescue him. The Byzantines were again defeated, with both John and Branas taken prisoner. The victorious Franks and Armenians then conducted widespread plundering of the island, not sparing churches or convents. In the words of the historian
Steven Runciman, "The crops were burnt; the herds were rounded up, together with all the population, and driven down to the coast. The women were raped; children and folk too old to move had their throats cut". The rape of the island lasted for three weeks, before Raynald and Thoros re-embarked their men upon the news of the approach of a Byzantine fleet. John and Branas were taken in captivity to
Antioch until he was ransomed. This was done at some unknown point, as John took part in a church council in the
Palace of Blachernae in May 1157. In 1158 John accompanied Manuel on his campaign in
Cilicia; his presence is attested at the reception of King
Baldwin III of Jerusalem at
Mopsuestia. John is then attested as attending church synods at Constantinople in March 1166, as well as January–February 1170. When John's son-in-law,
Amalric of Jerusalem, visited Constantinople in March 1171, John was detailed to welcome him on Byzantine territory and accompany him to the Byzantine capital. John then took part in the campaign against the Seljuks that led to the
Battle of Myriokephalon. The Byzantines were defeated and John was killed during the battle, shortly after 17 September 1176. ==Family==