Byzantine emperor from 715 to 717. He was an obscure tax collector of southwestern Asia Minor who against his will was proclaimed emperor by the troops of the Opsikion theme rebelling against Anastasius II. His supporters successfully captured Constantinople, and Anastasius was deposed and entered a monastery. Theodosius was quite unsuited to imperial office and in 717 was forced to abdicate by the able commander of the Anatolikon troops, Leo III the Isaurian, and ended his life in a monastery at Ephesus.