John Doukas (general under Manuel I)
John Doukas was a Byzantine general in the reign of Emperor Manuel I Komnenos (1143–1180).
He was involved in the unsuccessful attempt at reconquering Southern Italy in 1155–56. Doukas was the second in command to Michael Palaiologos. While Palaiologos lived, they advanced the Byzantine cause, allying with Pope Adrian IV and Count Robert of Loritello to end the power of William the Bad in Apulia. After Palaiologos' death however the whole campaign fell apart and Doukas was eventually imprisoned in Palermo. He was freed from his Italian captivity in early 1158 as part of a treaty that he, while in captivity, helped negotiate between Byzantium and Sicily.
Sources
Norwich, John Julius. Byzantium: The Decline and Fall (New York: Alfred A. Knopf, 1996) p. 111-116.