Alexander I Karađorđević (Serbo-Croatian: Александар I Карађорђевић, romanized: Aleksandar I Karađorđević, pronounced [aleksǎːndar př̩viː karadʑǒːrdʑevitɕ]; 16 December [O.S. 4 December] 1888 – 9 October 1934), also known as Alexander the Unifier (Aleksandar Ujedinitelj / Александар Ујединитељ [aleksǎːndar ujedǐniteʎ]), 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 in 1934. His reign of 13 years is the longest of the three monarchs of the Kingdom of Yugoslavia.
Born in Cetinje, Montenegro, Alexander was the second son of Peter and Zorka Karađorđević.