Isidore of Kiev

Isidore of Kiev, also known as Isidore of Thessalonica, was a prominent prelate of Byzantine Greek origin, born in the year one thousand three hundred eighty-five. His ecclesiastical journey saw him rise to the position of metropolitan of Kiev and all Rus' from one thousand four hundred thirty-seven to one thousand four hundred forty-one, a role he undertook after being appointed by Joseph II of Constantinople.

A staunch advocate for the union with Rome, Isidore left Moscow to participate in the Council of Ferrara–Florence. Upon his return in one thousand four hundred forty-one, he faced imprisonment due to his beliefs but managed to escape later that same year. In a significant turn of events, a council of Russian bishops elected their own metropolitan in one thousand four hundred forty-eight, effectively declaring the autocephaly of the Russian Orthodox Church. Despite this, Isidore retained recognition from Constantinople as metropolitan until one thousand four hundred fifty-eight, when Gregory the Bulgarian was appointed as the first metropolitan of the Uniate church.

In the years that followed, Isidore was sent back to Constantinople, where he famously proclaimed the union of the Greek and Latin churches at the Hagia Sophia on the twelfth of December in one thousand four hundred fifty-two. After the fall of Constantinople, he returned to Rome, where he continued to serve in various high-ranking positions within the Latin Church, including cardinal bishop of Sabina, Archbishop of Cyprus, Camerlengo of the Sacred College of Cardinals, and Latin Patriarch of Constantinople.