Leo III, Leon III, or Levon III may refer to:
People Leo III the Isaurian (685–741), Byzantine emperor 717–741 Pope Leo III (d. 816), Pope 795–816 Leon III of Abkhazia, King of Abkhazia 960–969 Leo II, King of Armenia (c. 1236–1289), sometimes referred to as Leo III, ruled from 1269 to 1289. Leo III, King of Armenia (1287–1307), ruled from 1303 to 1307
Other uses Leo A, an irregular galaxy in the constellation of Leo The Oath of Leo III, 16th-century painting about the 9th century Pope Leo III LEO III (computer), an early computer used for commercial business applications
tr:III. Leo