Isidore of Kiev

Isidore or Isidor of Kiev, also known as Isidore of Thessalonica (1385 – 27 April 1463), was a prelate of Byzantine Greek origin. From 1437 to 1441, he served as the metropolitan of Kiev and all Rus', based in Moscow, after being chosen by Joseph II of Constantinople.

As a supporter of the union with Rome, he left Moscow to attend the Council of Ferrara–Florence. On his return in 1441, he was imprisoned but allowed to escape later that year. A council of Russian bishops chose their own metropolitan in 1448, which amounted to a declaration of autocephaly by the Russian Orthodox Church. However, Isidore continued to be recognized by Constantinople as metropolitan until 1458, when Gregory the Bulgarian was made the first metropolitan of the Uniate church.

Isidore was later dispatched to Constantinople and he proclaimed the union of the Greek and Latin churches at the Hagia Sophia on 12 December 1452. Following the fall of Constantinople, he returned to Rome. In the Latin Church, Isidore was the cardinal bishop of Sabina, Archbishop of Cyprus, Camerlengo of the Sacred College of Cardinals and the Latin Patriarch of Constantinople.