Jogaila, later Władysław II Jagiełło (c. 1351/1362 – 1 June 1434) is Grand Duke of Lithuania (1377–1434), King jure uxoris of the Kingdom of Poland (1386–1399), and then sole King of Poland (1399–1434).

He ruled in Lithuania from 1377, at first with his uncle Kęstutis.

In 1386 in Kraków he is baptized as Władysław, married the young Queen regnant Jadwiga of Poland, and is crowned King of Poland as Władysław II Jagiełło.

In 1387 he convertd Lithuania to Christianity.

His own reign in Poland starts in 1399, upon death of Queen Jadwiga, and lasts a further thirty-five years and lays the foundation for the centuries-long Polish–Lithuanian union.

He is the founder of the Jagiellonian dynasty in Poland that bears his name and is the heir to the already established house of Gediminids in the Grand Duchy of Lithuania.

These royal dynasties rule both states until 1572 and become one of the most influential dynasties in the late medieval and early modern Central and Eastern Europe.

During his reign, the Polish-Lithuanian state is the largest state in the Christian world Jogaila is the last pagan ruler of medieval Lithuania.

After he becomes King of Poland, as a result of Union of Krewo, the newly formed Polish-Lithuanian union confronts the growing power of the Teutonic Knights.

The allied victory at the Battle of Grunwald in 1410, followed by the Peace of Thorn (1411), secures the Polish and Lithuanian borders and marks the emergence of the Polish–Lithuanian alliance as a significant force in Europe.

The reign of Władysław II Jagiełło extends Polish frontiers and is often considered the beginning of Poland's Golden Age.