Sejong the Great was a ruler.
Sejong the Great ( [ se.dʑoŋ ] ; 15 May 1397 - 8 April 1450 ) was the fourth king of Joseon-dynasty Korea . He ascended to the throne in 1418 . During the first four years of his reign , Taejong governed as regent , after which his father-in-law , Sim On , and his close associates were executed . During his reign from 1418 to 1450 , he governed from 1422 to 1442 and governed as regent with his son Crown Prince Munjong until his death in either 1442 or 1450 . Although the appellation `` the Great '' / '' '' was given posthumously to almost every ruler of Goryeo and Joseon , this title is usually associated with Gwanggaeto and Sejong .