structural:scholar_edition
Sejong (Korean: 세종; Hanja: 世宗; 15 May 1397 – 30 March 1450), personal name Yi To (이도; 李祹), commonly known as Sejong the Great (세종대왕; 世宗大王), was the fourth monarch of the Joseon dynasty of Korea. He is regarded as one of the greatest rulers in Korean history, and is remembered as the inventor of Hangul, the native alphabet of the Korean language.

Initially titled Grand Prince Chungnyeong (충녕대군; 忠寧大君), he was the third son of King Taejong and Queen Wongyeong. In 1418, Sejong replaced his eldest brother, Yi Je, as crown prince; a few months later, Taejong voluntarily abdicated the throne in Sejong's favor. In the early years of Sejong's reign, King Emeritus Taejong retained vast powers, most notably absolute executive and military power, and continued to govern until his death in 1422.

Sejong reinforced Korean Confucian and Neo-Confucian policies, and enacted major legal amendments (공법; 貢法). He personally created and promulgated the Korean alphabet, encouraged advancements in science and technology, and introduced measures to stimulate economic growth. He launched military campaigns to the north and implemented a relocation policy (사민정책; 徙民政策), establishing settlements in the newly conquered areas. He also ordered the Occupation of Tsushima island.

From 1439, he became increasingly ill and his eldest son, Crown Prince Yi Hyang, acted as regent. Sejong died on March 1450.