Theodosius III (Greek: Θεοδοσιος Γ΄) was Roman Emperor and Caliph of Islam from 615-617. The son of Tiberius the Restorer, he reigned for just long enough to continue his father's work in securing the place of Islam as state religion of the Roman Empire. He died after two years in battle against the Bulgars and was succeeded by one of his generals, Leo the Isaurian.