Boris I of Bulgaria
In 863, a mission from the Patriarch of Constantinople converted Tsar Boris I of Bulgaria to Christianity. Boris realized that the Christianization of his subjects by the Byzantine mission would facilitate the undesired spread of Byzantine influence in Bulgaria, as the liturgy was carried out in the Greek language, and the newly established Bulgarian Church was subordinate to the Church of Constantinople. A popular revolt against the new religion prompted the king to request that the Bulgarian Church be granted independence by Constantinople.