King Sejong the Great

The fourth king of the Joseon dynasty, Sejong reigned from 1418 to 1450 and presided over what is conventionally regarded as the high point of traditional Korean scholarship and statecraft. Born in 1397, he was the third son of King Taejong, the dynasty's third monarch. Taejong set aside his eldest son as heir in Sejong's favor and abdicated in 1418, though he retained control of military affairs until his death in 1422. It was under this arrangement that a Korean expedition was sent against the pirate bases of Tsushima Island in 1419.

Sejong's most enduring achievement was the creation of Hangul, the Korean alphabet. Until the fifteenth century, Korean had been written with Chinese characters, a system poorly suited to the language and accessible only to the educated elite. The new script, promulgated in 1446 in a document titled Hunminjeongeum ("the correct sounds for the instruction of the people"), used a small set of letters whose shapes reflected the articulation of the sounds they represented. Though resisted by parts of the scholarly class, it eventually became the standard writing system of Korea and remains in universal use.

The reign was also notable for state-sponsored science and technology. Sejong expanded the Hall of Worthies (Jiphyeonjeon), a royal research institute that supported the alphabet project and produced works on agriculture, medicine, geography, and history. Court inventors and astronomers, the most famous being Jang Yeong-sil, developed water clocks, sundials, astronomical instruments, and a standardized rain gauge used to assess harvests for taxation. The agricultural manual Nongsa jikseol, compiled in 1429, gathered farming techniques suited to Korean conditions rather than relying on Chinese models.

In foreign and military policy, Sejong pushed the kingdom's northern frontier to roughly the line of the Yalu and Tumen rivers, establishing fortified districts known as the four forts and six posts against Jurchen incursions; this frontier broadly corresponds to the present northern border of Korea. His health declined in his later years, and he died in 1450, succeeded by his eldest son Munjong. Later generations accorded him the epithet "the Great," a distinction shared by few Korean monarchs.