Casimir Jagiellon was the third and youngest son of King Władysław II Jagiełło and his fourth wife, Sophia of Halshany. His father was already 65 at the time of Casimir’s birth, and his brother Władysław III, three years his senior, was expected to become king before his majority. Strangely, little was done for his education; he was never taught Latin, nor was he trained for the responsibilities of office, despite the fact he was the only brother of the rightful sovereign. He often relied on his instinct and feelings and had little political knowledge, but shared a great interest in the diplomacy and economic affairs of the country. Throughout Casimir's youth, Bishop Zbigniew Oleśnicki was his mentor and tutor, however, the cleric felt a strong reluctance towards him, believing that he would be an unsuccessful monarch following Władysław's death.