Excerpts from Books and Wikipedia
"At this time, the Eastern Byzantine Empire was ruled by a woman, the empress Irene (r.791-802), whose authority the pope did not recognize. Although Pope Leo had no power to confer the imperial title, he seemingly took advantage of the Frankish king's presence in Rome to create a new Roman Catholic emperor in the west--one who would strengthen papal influence in Italy. Charlemagne, a devout Christian, was in the thirty-second year of his reign by this date, and had already made himself ruler of most of western Europe. He is often regarded as the first Holy Roman Emperor." [1001 Days]