Jogaila (jɔˈɡâːɪɫɐ; 1352/1362 - 1 June 1434), later Władysław II Jagiełło (vwaˈdɨswaf jaˈɡjɛwwɔ), was Grand Duke of Lithuania (1377–1434) and then King of Poland (1386–1434), first alongside his wife Jadwiga until 1399, and then sole ruler of Poland. Born a pagan, he converted to Catholicism in 1386 and was baptized as Ladislaus (Władysław) in Kraków, married the young Queen Jadwiga, and was crowned King of Poland as Władysław II Jagiełło. In 1387, he converted Lithuania to Catholicism. His own reign in Poland started in 1399, upon the death of Queen Jadwiga, lasted a further thirty-five years, and laid the foundation for the centuries-long Polish–Lithuanian union. He was a member of the Jagiellonian dynasty in Poland that bears his name and was previously also known as the Gediminid dynasty in the Grand Duchy of Lithuania. The dynasty ruled both states until 1572, and became one of the most influential dynasties in late medieval and early modern Europe.
Jogaila was the last pagan ruler of medieval Lithuania. After he became King of Poland, as a result of the Union of Krewo, the newly formed Polish-Lithuanian union confronted the growing power of the Teutonic Order. The allied victory at the Battle of Grunwald in 1410, followed by the Peace of Thorn, secured the Polish and Lithuanian borders and marked the emergence of the Polish–Lithuanian alliance as a significant force in Europe. The reign of Władysław II Jagiełło extended Polish frontiers and is often considered the beginning of Poland's Golden Age.
Little is known of Jogaila's early life, and even his year of birth is uncertain. Previously historians assumed he was born in 1352, but some recent research suggests a later date—about 1362. He was a descendant of the Gediminid dynasty and was the son of Algirdas, Grand Duke of Lithuania, and his second wife, Uliana of Tver, who was the daughter of the Rurikid prince Alexander of Tver. His name had a meaning of more courageous and superior than others, he spent most of his early time in Vilnius, at his father's manor.