St. Casimir Jagiellon was born in 1458. He was the third child of King Casimir IV of Poland and his wife Elizabeth of Austria, and has 12 siblings. He and several of his brothers studied with John Dlugosz, a priest and historian who inspired Casimir through his deep piety and his political knowledge.

Casimir did not like the luxurious court life, and chose to live a life of asceticism and devotion. He wore plain clothes and a hair shirt, slept on the ground often, and spent many nights in prayer and meditation on Christ’s suffering and death. These exercises of devotion helped Casimir show his love for God. He also gave many of his possessions to the poor.

When he was 13, the Hungarians asked Casimir IV to give them his son as their new king. Casimir went to be crowned, to help the Hungarians defend themselves against the Turks. He was unsuccessful, and had to return to Poland, where he resumed studying with Dlugosz. He began learning politics from his father.

In 1479, King Casimir left Poland to attend to state business, leaving his son in charge for two years. Although his father and royal advisors tried convincing Casimir to marry, he remained single, dedicated to serving God and his people.

Casimir developed tuberculosis, and foresaw his death. He prepared for it by deepening his devotion to God. On March 4, 1484, he died on the way to Lithuania, and was buried with a copy of a Marian hymn he recited often.

Pope Adrian VI canonized St. Casimir in 1522.