(also Jagello; Lithuanian, Jogaila). Born circa 1350; died June 1, 1434. Grand duke of Lithuania, except for a brief period, from 1377 to 1392. As Władyslaw II Jagiello, king of Poland from 1386. Founder of the Jagiellonian dynasty.
Jagiełło, a son of Algirdas, carried on a struggle in the Grand Duchy of Lithuania with his uncle Kestutis that ended in 1382 with the latter’s imprisonment and murder; Jagiello was aided in the struggle by the Teutonic Order. His marriage with the Polish queen Jadwiga resulted in the union of Poland and Lithuania under the Krewo Union of 1385. In 1392 opposition to the union on the part of the Lithuanian feudal lords forced Jagiello to surrender power in Lithuania to Vytautas (Polish, Witold). Jagiello proved himself a gifted organizer and military commander in the preparations for the Great War of 1409–11 against the Teutonic Order and in the battle of Tannenberg of 1410, where he commanded the combined Polish-Lithuanian-Russian army.