Final answer:
The bishop of Rome who claimed supremacy over all other Christians is known as the pope. Gregory I, also known as Gregory the Great, was one of the first bishops of Rome to claim this authority.
Step-by-step explanation:
The bishop of Rome who claimed supremacy over all other Christians is known as the pope. One of the first bishops of Rome to claim this authority was Gregory I, also known as Gregory the Great. He slowly asserted his authority through relationships with kings and overseeing the expansion of Christian missionary work. While the pope's authority was not initially recognized by all Christians, it eventually became at least nominally in place.