Leo was the son of Constantine V by his first wife, Eirene, daughter of the Khazar Khan. He crowned his five-year-old son, Constantine VI, in an elaborate ceremony in St. Sophia on Easter Day 776. This led to the revolt of five of Leo's half-brothers, who were no longer second in the order of precedence. Two of these brothers, Nikephoros and Christopher, had been elevated to the rank of Caesar in 769, and were thus their brother's heirs until the coronation of Constantine. Leo sent campaigns under Michael Lachanodrakon against the Arabs, but the latter were nevertheless successful with major incursions in 776, 779, and 780. Leo pursued a more lenient Iconoclast policy than his father had, and ended the active persecution of Iconophiles. Leo died in 780 while on campaign with his troops.
The design of the aniconic seals of Leo III, Leo IV, and Leo V are nearly indistinguishable. Although on coins attribution is aided by the appearance of the inscription basilis Romaion on miliaresia of Leo V, this appears on seals as early as the reign of Leo III. The shape of the cross is the best way to attribute both seals and coins: the horizontal bar becomes narrower the later the date. The seal shown above was issued after the coronation of Leo's son Constantine in 776. For more seals of the Isaurian Dynasty see the Dynasties of Empire section.