Ladislaus IV, 1595–1648, king of Poland (1632–48), son and successor of Sigismund III. His reign was marked by struggles with his subjects and wars with the Swedes, the Russians, and the Ottomans. Ladislaus in his later years vainly sought to establish authority over the nobles. The Cossack revolt, under Chmielnicki, broke out just before his death. He was succeeded by his brother, John II.