Sejong the Great

Born in 1397, the third son of the future King Taejong, Sejong was considered more gifted than his troubled older brother, the crown prince. In mid-1418, the crown prince was deposed and Sejong was elevated; months later, his father abdicated and Sejong took the throne at twenty-one. His reign became a high-water mark: he reestablished the Hall of Worthies in 1420, a research body that produced Korea's first native calendar, a 365-volume medical encyclopedia, and key agricultural texts. He led a successful invasion of Tsushima Island in 1419, then brokered decades of peace with Japan; he pushed Korea's northern border to roughly its present line through campaigns against raiding Jurchens; he overhauled tax and land policy, lifting agricultural output while cutting rates. He championed Confucianism publicly but remained privately Buddhist, a tension that set him against his own court in later years. Chronic illness forced him to hand daily governance to the crown prince in 1445. He died in 1450 at fifty-two, and South Korea has honored him ever since - a city bears his name, his face is on the currency, and Hangul is still the measure of his legacy.