Peter I of Serbia (d. 1921)
Peter I (Serbian Cyrillic: Петар I Карађорђевић, romanized: Petar I Кarađorđević; 11 July [O.S. 29 June] 1844 – 16 August 1921) reigned as the last king of Serbia (1903–1918) and as the first king of the Serbs, Croats and Slovenes (1918–1921). Since he was the king of Serbia during a period of great Serbian military success, he was remembered by the Serbian people as King Peter the Liberator, and also as Old King.

Peter was Karađorđe's grandson and third son of Persida Nenadović and Prince Alexander Karađorđević, who was forced to abdicate. Peter lived with his family in exile. He fought with the French Foreign Legion in the Franco-Prussian War. He joined as a volunteer under the alias Peter Mrkonjić in the Herzegovina Uprising (1875–77) against the Ottoman Empire.

He married Princess Zorka of Montenegro, daughter of King Nicholas, in 1883. She gave birth to his five children, including Prince Alexander. After the death of his father in 1885, Peter became head of the Karađorđević dynasty. After a military coup d'état and the murder of King Alexander I Obrenović in 1903, Peter became King of Serbia.

As king, he advocated a constitutional setup for the country and was famous for his liberal politics. The rule of King Peter was marked with the great exercise of political liberties, freedom of the press, national, economical and cultural rise, and it is sometimes dubbed a "golden" or "Periclean age".King Peter was the supreme commander of the Serbian army in the Balkan wars. Because of his age, on 24 June 1914, he proclaimed his son, Alexander, heir-apparent to the throne, as regent. In the First World War he and his army retreated across the Principality of Albania.