born Sept. 13, 1087
died April 8, 1143
Byzantine emperor (1118–43).
The son of Alexius I Comnenus , he made it his mission to reconquer Byzantine territory lost to the Arabs, Turks, and Crusaders. He cancelled Venetian trading privileges in the empire but was forced to restore them after the Venetians launched a fleet to retaliate against him. John allied himself with the German emperor against Roger II of Sicily (1130). He reconquered Cilicia (1137) and won homage from Antioch, but he failed to defeat the Syrian Turks.