Excerpts from Books and Wikipedia
"Irene of Athens . . . was Byzantine empress consort by marriage to Leo IV from 775 to 780, Byzantine regent during the minority of her son Constantine VI from 780 until 790, and finally sole empress regnant of the Byzantine Empire from 797 to 802. A member of the politically prominent Sarantapechos family, she was selected as Leo IV's bride for unknown reasons in 768. Even though her husband was an iconoclast, she harbored iconophile sympathies. During her rule as regent, she called the Second Council of Nicaea in 787, which condemned iconoclasm as heretical and brought an end to the first iconoclast period (730–787). As Irene's son Constantine reached maturity, he began to move out from under the influence of his mother. In the early 790s, several attempted revolts tried to proclaim him as sole ruler. In 797, Irene gouged out her son's eyes, maiming him so severely that he died a few days later. With her son dead, Irene proclaimed herself sole ruler." Pope Leo III decided to proclaim Charlemagne Holy Roman Emperor, assuming that Irene as a woman was not fit to rule and the throne of the Roman Empire was empty. [Wikipedia]