Mustafa III, 1717-73, Ottoman sultan (1757-73), son of Ahmed III. He succeeded his cousin Osman III to the throne of the Ottoman Empire (Turkey). The chief event of his reign was the war of 1768-74 with Russia (see Russo-Turkish Wars), which ended disastrously for Turkey (see Kuchuk Kainarji, Treaty of). His brother Abd al-Hamid I succeeded him in Jan., 1774.