JOHN VI. or V. (c. 1292-1383), surnamed Cantacuzene, East Roman emperor, was born at Constantinople. Connected with the house of Palaeologus on his mother's side, on the acces sion of Andronicus III. (1328) he was entrusted with the supreme administration of affairs. On Andronicus' death in 1341, Canta cuzene was left regent, and guardian of his nine year old son John Palaeologus. Being suspected by the empress and opposed by a powerful party at court, he rebelled, and got himself crowned emperor at Didymoteichos in Thrace, while John Palaeologus and his supporters maintained themselves at Constantinople. The civil war which ensued lasted six years, during which the rival parties called in the aid of the Serbians and Turks, and engaged mercenaries of every description. It was only by the aid of the Turks, with whom he made a disgraceful bargain, that Canta cuzene brought the war to a termination favourable to himself. In 1347 he entered Constantinople in triumph, and forced his opponents to an arrangement by which he became joint emperor with John Palaeologus and sole administrator during the minority of his colleague. During this period, the empire, already broken up and reduced to the narrowest limits, was assailed on every side. There were wars with the Genoese, who had a colony at Galata and had money transactions with the court ; and with the Serbians, who were at that time establishing an extensive empire on the north-western frontiers ; and there was a hazardous alliance with the Turks, who made their first permanent settlement in Europe, at Callipolis in Thrace, towards the end of the reign (1354).
Cantacuzene was far too ready to invoke the aid of foreigners in his European quarrels ; and as he had no money to pay them, this gave them a ready pretext for seizing upon a European town. Heavy taxation caused discontent, and a strong party had always favoured John Palaeologus, who entered Constantinople at the end of 1354. Cantacuzene retired to a monastery (where he assumed the name of Joasaph Christodulus) and occupied himself in literary labours. He died in the Peloponnese and was buried at Mysithra in Laconia. His History in four books deals with the years 1320-1356.
Cantacuzene was also the author of a commentary on the first five books of Aristotle's Ethics, and of several controversial theologi cal treatises, one of which (Against Mohammedanism) is printed in Migne (Patrologia Graeca, cliv.). History, ed. pr. by J. Pontanus (1603) ; in Bonn, Corpus scriptorum hist. Byz., by J. Schopen (1828 1832) and Migne, cliii., cliv. See also Val Parisot, Cantacuzene, homme d'etat et historien (1845) ; E. Gibbon, Decline and Fall, ch. lxiii.; and C. Krumbacher, Geschichte der byzantinischen Literatur (1897) ; E. W. Brooks in Cambridge Medieval History, vol. iv.