Alexander I Karađorđević (Cetinje, 16. December 1888 - Marseille, 9. October 1934), also known as Alexander the Unifier, the first King of the Kingdom of Serbs, Croats and Slovenes, and later of the Kingdom of Yugoslavia (1929 - 1934), was the second son of King Peter I and Princess Zorka, daughter of the King of Montenegro Nikola I Petrović and Queen Milena.
He spent his childhood in Montenegro, and completed primary school in Geneva. He was educated at the Military School in Saint Petersburg, and later (1903) in Belgrade, when his father Peter I became King of Serbia. In 1909, Alexander became heir to the throne, when his brother, Prince George renounced his claim to the throne. On 24. June 1914 Alexander became Regent of Serbia because King Peter I stepped down from the throne due to illness.
During the First Balkan War (1912), Alexander, heir to the throne as commander of the First Army fought victorious battles in Kumanovo and Bitola, and later in 1913. during the Second Balkan War, the Battle of Bregalnica. During World War I, he was the supreme commander of the Serbian army in the battles at Cer and Kolubara (1914), when the Serbian army defeated the army of the Austro-Hungarian monarchy. After the occupation (1915), Regent Alexander together with the Serbian army crossed Albania. He was the supreme commander when the Serbian army made the breakthrough of the Salonika front and won the battle at Kajmakčalan.
On 1. December 1918. was signed the Act on the creation of the Kingdom of Serbs, Croats and Slovenes. The Regent Alexander was crowned after the death of King Peter I (16. August 1921), and in 1922. he married Princess Maria of Romania, with whom he had three sons - Peter, Tomislav and Andrej.
In the new state, King Alexander conducted an agrarian reform that abolished the feudal system in agriculture, carried out the colonization of the border area in Banat, Bačka, Old Serbia and Macedonia, and reorganized the public administration by forming nine regional units and the city of Belgrade. He is credited for the creation of the alliance „Little Entente“ (Kingdom of Serbs, Croats and Slovenes, Romania and Czechoslovakia). Because of constant conflicts between Croatian and Serbian political parties, the King introduced dictatorship on 6. January 1929. and abolished the constitution. The same year, the Kingdom of Serbs, Croats and Slovenes got a new name „Kingdom of Yugoslavia“. The dictatorship lasted until 1931. when was declared the new constitution, the so called „forced constitution“.
During his visit to France, on 9. October, the King Alexander I was killed in Marseilles by the Croatian fascist and terrorist organization Ustaše and the Internal Macedonian Revolutionary Organization (VMRO). He was buried at Oplenac, in the Memorial Church of St. George, which has been built by his father King Peter I.
