Peter (Petar) Karađorđević (June 29, 1844 – August 16, 1921) became Serbia's first constitutional monarch in the aftermath of the 1903 military coup that resulted in the overthrow of the Obrenović dynasty, returning from exile to take his place as King. Nikola Pašić served as his Prime Minister.

Peter was born in Belgrade. The date of his birth is July 11 in the Julian calendar. In the intervening years before his appointment as King, Peter had served with the French during the unsuccessful Franco-Prussian War of 1870-71 and, in 1875, joined the Bosnian insurrection against the Ottomans. He married Princess Zorka of Montenegro on 1 August 1883 and together had four children prior to Zorka's early death in 1890.

The first years of King Peter's reign saw reforms to the constitution, the army and the school system, as well as improvements to the system of agriculture.

With the outbreak of war in Europe only a month away, and with Serbia in civil turmoil following the successful outcome of the Balkan Wars, both civil and military authorities demanded that Macedonia be administered by Serbia and in June 1914 Peter passed executive control of government to his second son Alexander, who became Regent on grounds of increasing ill health.

With Serbia's defeat towards the close of 1915 at the hands of combined Austro-Hungarian, German and Bulgarian forces led by August von Mackensen, King Peter had to be carried, along with similarly ill marshall Radomir Putnik, through the snow-covered mountains of Albania to Corfu.

On December 1, 1918, Peter reappeared briefly to accept his position as monarch of the newly declared Kingdom of the Serbs, Croats and Slovenes, which was to become Yugoslavia. With his death in 1921 Alexander became King.