Isidore was an ethnic Greek born in Thessaloniki during the latter part of the 1290s where he became a teacher and spiritual guide.
Career
As a disciple of St. Gregory, he was drawn into the dispute between the followers of Gregory Palamas and Barlaam of Calabria over Hesychasm during the middle decades of the fourteenth century.
In February 1347, during a synod convened by emperor John VI Kantakouzenos, Patr. John XIV was deposed and Isidore brought back and elected to succeed John XIV as patriarch of Constantinople. Upon becoming patriarch, Isidore released Gregory Palamas from prison and consecrated him Archbishop of Thessalonica.
Patriarchate
During the two and a half years of his patriarchate, Isidore sought to have the whole Byzantine Church accept the Palamite dogmas. He selected bishops only from the Palamite party. He instituted harsh penalties for those who refused to submit.[2]
3. Evangelos C. Pringipakis, "Patriarch Isidore I Boucheiras (± 1290 - 1350) in the Writtings of Demetrius Cydones", Byzantinos Domos 29 (2021), s. 417-439.