Alexander I of Yugoslavia

Alexander I Karađorđević (Serbo-Croatian: Александар I Карађорђевић, Aleksandar I Karađorđević, 16 December [O.S. 4 December] 1888 – 9 October 1934) 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.

Born in Cetinje, Montenegro, Alexander was the second son and fourth child of Peter and Zorka Karađorđević. The House of Karađorđević had been deposed in Serbia 30 years earlier by the rival House of Obrenović, and Alexander spent his early life in exile with his father in Montenegro and later Switzerland. He subsequently moved to the Russian Empire and enrolled in the imperial Page Corps. Following the May Coup and the assassination of King Alexander I Obrenović in 1903, Peter ascended the Serbian throne. In 1909, Alexander's elder brother, Prince George, renounced his succession rights, making Alexander heir apparent. Alexander distinguished himself as a field commander during the Balkan Wars, leading Serbian forces to victories over the Ottoman Empire and the Bulgarians. In 1914, he was appointed prince regent after his father transferred his royal duties due to ill health. During the First World War, he held nominal supreme command of the Royal Serbian Army.