Tsar Simeon the Great. Simeon was born in 864 or 865, as the 3rd son of Knyaz Boris I. As Boris was the ruler who Christianized Bulgaria, Simeon was a Christian all his life. Because his eldest brother Vladimir was heir to the throne, Boris intended Simeon to become a cleric, possibly Bulgarian archbishop, and sent him to the leading University of Constantinople to receive theological education when he was 13 or 14. He took the name Simeon as a novice in a monastery in Constantinople.