King Władysław II Jagiełło was a significant historical figure who ruled as the Grand Duke of Lithuania and later as the King of Poland from 1386 to 1434. He was born around 1351 and was a member of the Gediminas dynasty. Jagiełło is best known for his role in the Union of Krewo, which united Poland and Lithuania, strengthening both nations against external threats. Jagiełło's reign is marked by the famous Battle of Grunwald in 1410, where his forces defeated the Teutonic Knights, a powerful military order. This victory was crucial in establishing Polish-Lithuanian dominance in the region. His leadership helped to foster a period of cultural and political growth, laying the foundation for the future Polish-Lithuanian Commonwealth.