Byzantine emperor from 741 to 775, son of Leo III the Isaurian.

Constantine was made coruler of the empire with his father in 720. Most of his life before and after his accession as sole ruler was spent in largely successful military campaigns against Arabs and Bulgars who threatened the empire. Because the empire's resources were thus engaged, the Lombards were able to take the exarchate of Ravenna in Italy (751), thus ending Byzantine influence in north and central Italy and indirectly fostering the historic alliance between the papacy and the Franks. Constantine was a strong Iconoclast (one opposed to the veneration of religious images) and was remembered by contemporaries for his persecution of monks who opposed his iconoclastic position. His military achievements won him great popularity, nonetheless, and were appreciated by later historians. He died in the Balkans while on a campaign against the Bulgarian kingdom.