John VI Kantakouzenos

John VI Kantakouzenos or Cantacuzene was a Byzantine Greek emperor and nobleman, statesman, and general. He served as grand domestic under Andronikos III Palaiologos and regent for John V Palaiologos before reigning as Byzantine emperor in his own right 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 remainder of his life as a monk and historian. At age 90 or 91 at his death, he was the longest-lived of the Roman emperors. His two disastrous civil wars led to the loss of much of the remaining territory in the Balkans under Byzantine control to the Serbian and Bulgarian empires, but the most severe loss during his civil war was the loss of the Gallipoli peninsula to the Ottoman Turks, allowing the Ottomans to gain territory in Europe and setting the stage for the destruction of the Byzantine Empire a century later.