Peter I, 1844–1921, king of Serbia (1903–18) and king of the Serbs, Croats, and Slovenes (1918–21), son of Prince Alexander of Serbia (Alexander Karadjordjević). He was brought up in exile in Geneva and Paris while the Obrenović line ruled Serbia, and he fought in the French army in the Franco-Prussian War (1870–71). In 1875, he joined the Bosnian insurrection against the Ottomans. The assassination (1903) of King Alexander of Serbia brought Peter to the throne. Peter proved an able and conscientious ruler and restored dignity to the court of Belgrade. He reformed the constitution, the army, and the school system and fostered improved methods of agriculture. The outstanding figure of his reign was Nikola Pašić, who directed Serbian policy in the Balkan Wars (1912–13) and in World War I. Early in 1914 Peter, who was in ill health, retired from active rule and his son, later King Alexander of Yugoslavia, became regent. Peter took part in the retreat (1915–16) of the Serbian troops through Albania to Corfu. In 1918 he was chosen to rule the Kingdom of the Serbs, Croats, and Slovenes (later known as Yugoslavia), while his son and successor remained regent.