(3 October 1458 – 4 March 1484) was a prince of the Kingdom of Poland and of the Grand Duchy of Lithuania. Second son of King Casimir IV Jagiellon. He became known for his piety, devotion to God, and generosity towards the sick and poor. He became ill (most likely with tuberculosis) and died at the age of 25. He was buried in Vilnius Cathedral and his cult grew. His canonization was initiated by his brother King Sigismund I the Old in 1514 and the tradition holds that he was canonized in 1521.

Saint Casimir - Wikipedia