Sejong the Great (1397 ¡V 1450) fourth ruler of the Joseon Dynasty of Korea. He was the third son of King Taejong and Queen Wongyeong, and was designated as Crown Prince after his older brother, Grand Prince Yangnyeong, was stripped of his title. He ascended to the throne in 1418, but during the first four years of his reign, Taejong governed as regent and executed Sejongs father-in-law, Shim On, and his close associate..