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.