John II Casimir Vasa (Polish: Jan II Kazimierz Waza; Lithuanian: Jonas Kazimieras Vaza; 22 March 1609 – 16 December 1672) was King of Poland and Grand Duke of Lithuania from 1648 to his abdication in 1668 as well as a claimant to the throne of Sweden from 1648 to 1660. He was the first son of Sigismund III Vasa with his second wife Constance of Austria. John Casimir succeeded his older half-brother, Władysław IV Vasa.
As a prince, John Casimir embarked at Genoa for Spain in 1638 to negotiate a league with Philip IV against France, but was captured by Cardinal Richelieu and imprisoned at Vincennes where he remained for two years. He was released when his brother, Władysław IV, promised never to wage war against France. John Casimir then travelled extensively throughout western Europe and entered the order of Jesuits in Rome in 1643. He was made cardinal by Innocent X, but after returning to Poland, he became a layman and succeeded his brother in 1648. His reign commenced amid the confusion and disasters caused by the great revolt of the Cossacks under Bohdan Khmelnytsky in Ukraine, who had advanced into the very heart of Poland. The power of the king had been stripped of almost all its prerogatives by the growing influence of the nobles.
