Sejong (1397-1450) was a Korean king and inventor of the Korean alphabet. His long reign, 1418-1450, is generally acknowledged to have been the most brilliant period of the Yi dynasty.

Sejong, formally named Yi To, and known as Prince Ch'ungnyong before taking the throne, was born on May 7, 1397. Since his eldest brother, Prince Yangnyong, had been designated crown prince in 1404, Sejong in early life did not anticipate the throne. But Yangnyong's erratic behavior led to his deposition and Sejong's elevation in July 1418. (An unofficial tradition holds that Prince Yangnyong feigned instability so that Sejong might rule.) Sejong became king, following his father's abdication, on Sept. 7, 1418.

During his reign Sejong introduced improved administrative procedures, new census laws, penal reforms, and some civil rights for slaves and outcast groups. He maintained proper relations with China and a firm stance with Japan. His devastating attack on the island of Tsushima in 1419, in retaliation for the coastal raids of Japanese pirates, eliminated the immediate peril and ultimately led to a treaty (1443) which established a long-lasting, peaceful relationship with Japan. To the north he incorporated new territory south of the Yalu and Tumen rivers, which until then had been occupied or threatened by the Jürchen barbarians. Korea's modern borders are thus one of his legacies.

In the cultural field, Sejong ordered the compilation of outstanding historical works, and his system of branch depositories for historical records ensured the survival of many valuable books through the destructive Japanese invasions of 1592-1598. He reformed the court music. Voluminous encylopedias of agriculture, medicine, military science, and public administration were compiled. He sponsored the compilation of gazeteers, instituted standardized weights and measures, and installed rain gauges throughout the country, all of which contributed to his rationalization of tax-assessing procedures. His researchers designed clepsydras, armillary spheres, and other scientific instruments.

Sejong's greatest achievement was the alphabet. It was first announced late in 1443 and formally proclaimed in 1446. Sejong was not merely the patron of this alphabet but its actual theoretician and inventor. It reflects in its structure and graphic symbolism a very sophisticated understanding of linguistics. Although the script was coolly received by his officials and did not for many years completely replace the classical Chinese in which they wrote, it was a long-run success and is today the writing system of all Koreans.

Sejong was quick to promote those who showed promise; especially intelligent young men received his "reading vacations," paid leaves for untrammeled study. The most promising scholars were appointed to the famous "College of Assembled Worthies" (organized 1420), where the research for his cultural and technical projects was done. Many of their publications survive today and reveal a uniformly high standard of scholarship. Sejong's friendship with his scholars was legendary. In political life too he got on well with his highest officers.

But beginning in the late 1430s, Sejong's relations with his officials became strained over two issues. The first was his attempt to delegate certain royal duties to the crown prince in order to conserve his own health. From about 1437, Sejong suffered from rheumatism and diabetes, and about 1442 his eyesight also began to fail. He repeatedly asked his ministers' assent to his plans for the crown prince; just as regularly this assent was withheld. (Korean kings, while theoretically all-powerful, were by tradition and practice required to obtain a consensus of support for their actions.) The debate was resolved only in 1445, when the crown prince finally took over limited duties, but the ill feeling remained.

A second issue was Sejong's belief in Buddhism. The Yi dynasty had come to power partly as a reaction against the previous dynasty's excessive patronage of Buddhism, and from the beginning it had enforced strict limitations on the numbers of monks and monasteries and on tenable church property. As king, Sejong enforced these public policies, but personally he was a devout believer, especially after the death of his wife, Queen Sohon, in 1446. For this he suffered constant abuse from his Confucianist officials. Some of the opposition to his alphabet was doubtless a result of this antagonistic atmosphere.

Because of these struggles and his increasingly poor health, Sejong after 1446 began to turn from his official duties to his private pursuits. In addition to the assistance of the crown prince (later reigned as Munjong, 1450-1452), Sejong was helped by two other capable sons, Princes Anp'yong and Suyang (Sejo). Sejong spent his last years writing Buddhist devotional poetry, much of which still survives. Early in 1450, he left the palace and retired to the Seoul residence of his youngest son, where he died of a massive stroke on March 30, 1450.

Further Reading

• Sejong's reign is discussed in Takashi Hatada, A History of Korea, translated and edited by Warren W. Smith, Jr., and Benjamin H. Hazard (1969); and Woo-keun Han, The History of Korea, edited by Grafton Mintz (trans. 1970).
• King Sejong the Great: the light of fifteenth century Korea, Washington, D.C.: International Circle of Korean Linguistics, 1992.