https://en.wikipedia.org/wiki/Pope_Leo_III

Leo III (died 12 June 816) was the 96th pope from 26 December 795 to his death. Protected by Charlemagne from the supporters of his predecessor, Adrian I, Leo subsequently strengthened Charlemagne's position by crowning him emperor. The coronation was not approved in Constantinople, although the Byzantines, occupied with their own defenses, were in no position to offer much opposition.