John II Casimir Vasa, Polish king (d. 1672)
John II Casimir (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 until his abdication in 1668 as well as titular King of Sweden from 1648 until 1660. He was the first son of Sigismund III Vasa with his second wife Constance of Austria. His older half brother and predecessor on the throne was 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, however, 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.

The Tsardom of Russia and Sweden, which had long been active enemies of Poland, renewed their attacks. George II Rakoczy of Transylvania also invaded the Polish territory, while the Sejm was continuously dissolved due to abuse of the liberum veto law. Charles X Gustav of Sweden triumphantly marched through the country and occupied Kraków in 1655 forcing John Casimir to flee to Silesia. The Swedes were eventually stopped by Stefan Czarniecki under Częstochowa. The wars with the Swedes and Russians were terminated by treaties involving considerable cessions of provinces on the Baltic and the Dnieper on the part of Poland, which also lost its sway over the Cossacks who placed themselves under the protection of Russian Tsars. During these long battles, John Casimir, though feeble and of a peaceful disposition, frequently proved his patriotism and bravery.The intrigues of his wife in favor of the Duke of Enghien as successor to the Polish throne triggered a series of revolts, including a rebellion under Hetman Jerzy Sebastian Lubomirski. As a result, John Casimir abdicated at the Sejm of Warsaw on 16 September 1668. In the following year, he retired to France where he was hospitably treated by Louis XIV. John Casimir's reign was one of the most disastrous in the history of Poland. He was the third and last monarch on the Polish throne from the House of Vasa.