Leo III (685-741), also known as Leo the Isaurian and Leo the Syrian and whose original name was Konon, was born in the Syrian province of Commagene. He served under Emperor Justinian II when the emperor was attempting to reclaim his throne. After Justinian's victory, Leo was sent to fight against the Umayyad Caliphate, and was appointed as overall commander by Emperor Anastasius II.

Leo became ambitious, and conspired with his fellow commanders, to overthrow the new emperor, Theodosius III. He entered Constantinople in 717 and forced Theodosius to abdicate, and was crowned Leo III.