Joint rule as junior emperor with Constantine V (his father), 6 June 751 - 14 September 775 A.D.
Joint rule with Constantine VI (his son), 24 April 776 - 8 September 780 A.D.
Leo was the son of Constantine V by his first wife, Irene of Khazaria the daughter of a Khagan of the Khazars. He was crowned co-emperor by his father in 751. In 775 Constantine V died, leaving Leo as sole emperor. Leo, following the precedent set by his father and grandfather, appointed his son, Constantine VI, co-emperor. Leo's five half-brothers who had hoped to gain the throne rebelled by were defeated and exiled. The third Abbasid Caliph, Al-Mahdi, repeatedly invaded during Leo's reign but was repulsed by Leo's armies. Leo IV was raised as an iconoclast but, pursuing a path of conciliation, Leo allowed monks, persecuted and deported under his father, to return to their monasteries He was anointed as "Friend to the Mother of God" for allowing monks to retain images of the Theotokos. Leo also appointed an iconophile sympathizer as the patriarch of Constantinople. At the end of his reign, however, Leo reversed his stance of toleration. Leo died of fever while on campaign against the Bulgars. Constantine VI succeeded his father as emperor, ruling jointly with his mother, Irene.