This drama is about the life of the fourth king of the Joseon Dynasty of Korea, King Sejong who is considered the greatest king in Korean history for creating Hangul, the Korean alphabet and having many skilled followers such as Jang Yeong-sil. The Great King Sejong is a full scale politic drama describing how King Sejong and his loyal retainers cooperate and contrive to make his dynasty a better place. While King Sejong was in throne, the Chosun Dynasty enjoyed the most fortunate and happy age ever.