Casimir was the third son of King Casimir IV of Poland. Chosen by some Hungarian magnates as King of Hungary, as a rival to the already existing monarch (Matthias Corvinus), the Polish prince — who was then thirteen years old — was glad that the attempt to obtain the crown for him did not succeed, especially when he learned that it was not the Pope’s will for him to become king of an already established monarchy. Casimir served as regent of Poland while his father was in Lithuania.
His ascetic ideals made him reject the proposed marriage to a princess of the Empire, daughter of Frederick I. He died of tuberculosis at the age of twenty-five, in Grodno (Lithuania), on March 4, 1484, and was canonized by Leo X in 1521. He is the patron saint of Poland and Lithuania.
