CALLISTUS I, patriarch of Constantinople. At first a monk on Mount Athos, a convinced follower of the doctrine of Gregory Palamas, he succeeded Isidore I on the ecumenical see in 1350, occupying it until 1354–55, when he was forced to resign because he refused to crown Matthew Cantacuzenus, who had been associated with the empire by his father John. Since Matthew abdicated in 1357, C. resumed his functions, which he held until his death (1363). During his patriarchate, the Palamite Council of 1351 was held at the Blachernae Palace, which canonized the doctrine of Gregory Palamas. Antipalamite historians, such as Nicephorus Gregoras, portray C. as a narrow-minded and brutal figure whose zeal against opponents had to be moderated. He distinguished himself as a hagiographer and preacher.
Works by him include: 1) a Life of Gregory of Sinai (d. 1310), published by J. Pomjalovskij in St. Petersburg in 1894; 2) the Life of Theodore of Tirnovo, preserved only in Slavonic: cf. Byzantinische Zeitschrift, 15 (1906), p. 386; 3) a Panegyric of John the Faster, restorer of the Constantinopolitan monastery of Petra in the 11th century, edited by H. Gelzer, Kallistou Enkomion auf Joannes Nesterites, in Zeitschrift für Wissenschaftliche Theologie, 29 (1886), pp. 64–89; 4) an unpublished Sermonary containing 32 discourses and homilies, preserved in codex 8 of the Athonite monastery of Chilandar, from the 15th century; 5) a Panegyric of the Cross, published by I. Gretser in his collection De Cruce Christi (Ingolstadt 1600; in Opera omnia, II, Regensburg 1734, pp. 187–97); 6) a Homily on the Dormition of the Virgin, published in the journal Ἐκκλησιαστικὸς Φάρος, 8 (1911), pp. 114–49; the author does not express himself clearly on the Assumption proper; 7) a Sermon on the Beheading of St. John the Baptist, contained in codex theol. gr. 279 of the Austrian National Library in Vienna.