John VI Kantakouzenos

John VI Kantakouzenos, also rendered Cantacuzene, was a Byzantine nobleman, statesman and general who became emperor in his own right. He served as grand domestic under Andronikos III Palaiologos and as regent for John V Palaiologos before reigning as emperor from 1347 to 1354. Deposed by his former ward, he was forced to retire to a monastery under the name Joasaph Christodoulos and spent the rest of his life as a monk and historian, dying at ninety one, the longest lived of the Roman emperors. His two disastrous civil wars cost the empire much of its remaining Balkan territory to the Serbian and Bulgarian empires, and, most severely, the loss of the Gallipoli peninsula to the Ottoman Turks, which let the Ottomans gain their first territory in Europe and set the stage for the empire's destruction a century later.