Callistus II of Constantinople

Callistus II of Constantinople was a Byzantine Hesychast monk and spiritual writer who reigned as list of Ecumenical [Patriarchs of Constantinople|Ecumenical Patriarch of Constantinople] in 1397. He was Patriarch through the reign of the Byzantine Emperor Manuel II Palaiologos, and through his short Patriarchal reign, Constantinople was under siege by the Ottoman Sultan Bayezid I. Within the Orthodox Church, his memory is celebrated on November 22 (Eastern [Orthodox liturgics)|22 November].
His surname indicates that he was from the monastery of Xanthopoulos. The majority of Patriarchs in the 14th century were monks in the Hesychast tradition.