Sejong the Great ruled alongside his father up to 1422 .
To the south , he subjugated Japanese raiders and captured Tsushima Island ( known as Daemado in the Korean language ) .During his reign from 1418 to 1450 , he governed along with his father , the King Emeritus Taejong from 1418 to 1422 , then governing as the sole monarch from 1422 to 1450 .