Leo IV, called Chozar or the Khazar (c. 750 - 780), succeeded his father, Constantine V, as emperor of the Byzantine Empire in 775. In 776 he associated his young son, Constantine, with himself in the empire, and suppressed an uprising led by his five step-brothers which broke out as a result of this proceeding.
Like his father and grandfather, Leo was successful in battle against the Arabs and Bulgars. Unlike his father and grandfather, however, Leo favoured the iconophiles, and restored an iconophile patriarch.
During his reign Leo was largely under the influence of his wife Irene, and when he died suddenly in 780 she was left as the guardian of his son and successor, Constantine VI.
Leo the Fourth, the son of the fifth and the father of the sixth Constantine, was of a feeble constitution both of mind and body, and the principal care of his reign was the settlement of the succession.
The nuptials of Leo and Irene were celebrated with royal pomp; she soon acquired the love and confidence of a feeble husband, and in his testament he declared the empress guardian of the Roman world, and of their son Constantine the Sixth, who was no more than ten years of age.
Leo was alarmed at these signs of security and intelligence; but though he retired with silent steps, his entrance and departure were noticed by a slave who lay concealed in a corner of the prison.