John II Casimir (Polish: Jan II Kazimierz Waza; 22 March 1609 – 16 December 1672) was King of Poland and Grand Duke of Lithuania during the era of the Polish–Lithuanian Commonwealth, Duke of Opole in Upper Silesia, and titular King of Sweden 1648–1660. In Poland, he is known and commonly referred as Jan Kazimierz. His parents were Sigismund III Vasa (1566–1632) and Constance of Austria (1588–1631). His older brother, and predecessor on the throne, was Władysław IV Vasa. John Casimir's reign was one of the most disastrous in the history of Poland, whose dismemberment by the houses of Moscow, Brandenburg, and Habsburg, as it took place 100 years after his death, he predicted in a memorable speech to the diet of 1661. Related to the Habsburg rulers of the Holy Roman Empire, he was the third and last monarch on the Polish throne from the House of Vasa. He was the last ruler of Polish–Lithuanian Commonwealth bearing a blood connection to the Jagiellon dynasty. John Casimir was born in Kraków on 22 March 1609. His father, Sigismund III, the grandson of Gustav I of Sweden, had in 1592 succeeded his own father to the Swedish throne, only to be deposed in 1599 by his uncle, Charles IX of Sweden. This led to a long-standing feud wherein the Polish kings of the House of Vasa claimed the Swedish throne, resulting in the Polish–Swedish War of 1600–1629. Poland and Sweden were also on opposite sides in the Thirty Years' War (1618–1648). His mother, Queen Constance, was the daughter of Charles II of Austria and Maria Anna of Bavaria and also the younger sister of Ferdinand II, Holy Roman Emperor. In 1648 John Casimir was elected by the Polish Parliament to succeed his half-brother on the Polish throne. The reign of the last of the Vasa in the Polish–Lithuanian Commonwealth would be dominated by the Russo-Polish War (1654–1667).

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