Mustafa or Kara Mustafa (käräˈ mŏstäfäˈ) [key] [Turk. kara = black], d. 1683, Turkish grand vizier (chief executive officer) under Sultan Muhammad IV of the Ottoman Empire (Turkey). He succeeded his brother-in-law, Ahmed Köprülü. Ambitious and belligerent, he allied himself with the Hungarian rebels under Thököly against Holy Roman Emperor Leopold I and led the siege of Vienna in 1683. His military incompetence facilitated the relief of Vienna by King John III of Poland, and the besieging army, including Mustafa, fled in panic. Mustafa suffered several routs during his retreat through Hungary and, having reached Belgrade, was ordered to commit suicide by the sultan.