(Late 7th century-middle 8th century) Byzantine emperor 715-717.
The main challenge of his reign was an Umayyad invasion into Asia Minor and attacks along the coast.
It has been suggested that he was the son of former Emperor Tiberius 3.
Late 7th century: His year of birth cannot be set, although he had must have been old enough to have a son by the year of 717. He may well have been born any time between 650 and 690.
Becomes financial officer and tax collector.
715 May: Is declared emperor by the army in a rebellion against Anastasius 2.
November: Theodosius and his troops manage to take over Constantinople. Anastasius is deposed, but treated mildly by Theodosius. Anastasius flees to Nicaea, without having submitted to the new emperor.
716: Anastasius finally submits to the new emperor, and retires to a monastery in Thessalonica.
716: Accepts a peace deal with Bulgaria, aiming at freeing forces to defend the empire against Umayyad invasion.
717: Rebellion against Theodosius, led by Leo the Isaurian and Artabasdus (emperor 741-743).
March 25: Resigns as emperor after that Leo captures his son in Nicomedia. Both he and his son join the clergy.
729: Possibly, Theodosius becomes Bishop of Ephesus, although it may have been his son receiving this position.