Theodosios III was a Byzantine emperor who reigned from approximately 715 to 717. Originally a tax collector in Adramyttium, he was reluctantly elevated to the throne by the troops of the Opsician Theme following a revolt against Emperor Anastasius II. His brief rule occurred during a period of intense political instability known as the Twenty Years' Anarchy. After being challenged by Leo the Isaurian, Theodosios negotiated an abdication to protect his son and eventually retired to a monastery.