GREGORY MAMMAS. — Catholic Patriarch of Constantinople, successor of Metrophanes (d. 1443), also a Catholic. In 1451 he was forced to take refuge in Rome, where he died in 1459. G. participated in the Council of Florence in the years 1438–39 as vicar of the Greek Patriarch of Alexandria, as protosymbulus of the Patriarch of Constantinople, and as confessor to the Byzantine Emperor John VIII, who was present at that assembly. He subscribed to the bull of Union of 6 July 1439 and remained always faithful to the unity of the Roman Church; indeed, he became its defender with his two apologetic treatises directed against the bitter opponent Mark Eugenicus and with a theological writing addressed to the Emperor of Trebizond in defense of Catholic doctrine.
These three works have already been published, while three others, of which he himself speaks (PG 160, 198 C), remain unpublished; these also deal with the articles of faith defined in the bull of Union of the Greeks. G. M., of noble character, was highly esteemed by Popes Eugenius IV, Nicholas V, Callistus III, and Pius II. The latter left a written record of him, stating that he died «not without a reputation for holiness». His epitaph is known, but unfortunately his tomb, probably in S. Giorgio in Velabro in Rome, has not yet been discovered.