Gregory the Bulgarian

Born in Bulgaria, Gregory was an Eastern Orthodox Christian. He became an aide to Isidore, Metropolitan of Kiev and All Rus', who signed the act of union with the Roman Church on behalf of the Russian Church at the Council of Florence in 1439.

In 1458, he was appointed as the metropolitan of the newly-established Kiev see by the Uniate Patriarch Gregory Mammas of Constantinople. The Patriarch gave the new Metropolitan the title of the Metropolitan of Kiev, Galich and All Rus'. (Prior to that, in 1448, Russian bishops in Moscow, who had rejected the Union with Rome, elected Jonas as Metropolitan of Kiev and All Rus' without the consent from Constantinople.) The Polish-Lithuanian rulers accepted him, but he was rejected by the Grand Duchy of Moscow, whose metropolitans after 1461 abandoned the "Kiev" title and took on the new title of "metropolitan of Moscow and all Rus'".

The Kiev metropolinate within the Polish kingdom and the Great Lithuanian principality under the rule of metropolitan Gregory (1458–1472) remained therefore in communion with the Holy See, as well as during the rule of the following metropolitan Міsail (1476–1480).