The correct answer is - The emperor.
In the Byzantine Empire, the emperor was a monarch that had a complete authority, for both the empire's affairs and the religious affairs. So the emperor of the Byzantine Empire had the final word in everything, and apart from being the head of the empire, he was the head of the church as well and dictated the religious activities and politics in the empire, unlike in the west were the pope was in charge of the church activities and politics.
