Saint Casimir was a 15th-century prince of the Kingdom of Poland and the Grand Duchy of Lithuania. Born at Wawel Castle to King Casimir IV Jagiellon, he was the second son and eventually became the heir apparent to the throne. Although he participated in a military campaign in Hungary as a teenager, he was primarily recognized for his religious devotion, his charitable nature toward the impoverished, and his commitment to his studies. He died in Hrodna at the age of 25, likely from tuberculosis, and is honored as a patron of Lithuania and Poland.