Alexander I Karađorđević was King of the Serbs, Croats and Slovenes from 16 August 1921 to 3 October 1929 and King of Yugoslavia from 3 October 1929 until his assassination. His thirteen-year reign was the longest of the kingdom's three monarchs. He served as the de facto head of state of the Kingdom of Serbia from 1914 to 1918 and of Yugoslavia from 1918 to 1921 as prince regent for his father, Peter I.
