Constantine IV, called the Younger and sometimes incorrectly Pogonatos out of confusion with his father, was Byzantine Emperor from 668 to 685. His reign saw the first serious check to nearly 50 years of uninterrupted Islamic expansion, while his calling of the Sixth Ecumenical Council saw the end of the monothelitism controversy in the Byzantine Empire; for this, he is venerated as a saint in the Eastern Orthodox Church, with his feast day on September 3.