King Peter I, also known as Peter I of Serbia, was the king of Serbia from 1903 until 1918. He played a significant role in the Balkan Wars and World War I, advocating for Serbian independence and unity among South Slavic peoples. His reign marked a period of modernization and national awakening in Serbia. In 1918, after the war, King Peter I became the first king of the newly formed Kingdom of Serbs, Croats, and Slovenes, which later became known as Yugoslavia. He was known for his democratic ideals and efforts to promote peace and cooperation among the diverse ethnic groups in his kingdom.