Biography, His Life
Early life as a Child
Sejong was born on May 7, 1397, the third son of
 When he was twelve, he became Grand Prince Chungnyeong (충녕대군). As a young prince, Sejong excelled in various studies and was favored by King Taejong over his two older brothers.
As the third son of Taejong, Sejong's ascension to the throne was unique. Taejong's eldest son,
Yangnyeong (양녕대군), was named heir apparent in 1404. However, Yangnyeong's free spirited nature as well as his preference for hunting and leisure activities resulted in his removal from the position of heir apparent in June 1418. Though it is said that Yangnyeong abdicated in favor of his younger brother, there are no definitive records regarding Yangnyeong's removal. Taejong's second son Grand Prince Hyoryeong became a monk upon the elevation of his younger brother Sejong.
Following the removal of Yangnyeong as heir apparent, Taejong moved quickly to secure his youngest son's position as heir apparent. The government was purged of officials who disagreed with the removal of Yangnyeong. In August 1418, Taejong abdicated in favor of Sejong. However, even in retirement Taejong continued to influence government policy. Sejong's surprising political savvy and creativity did not become apparent until after Taejong's death in 1422.
Starting politics based on Confucianism
King Sejong revolutionized government by appointing people from different social classes as civil servants. Furthermore, he performed official government events according to
Confucianism, and he encouraged people to behave according to Confucianism. As a result, Confucianism became the social norm. He also published some books about Confucianism.
At first, he suppressed
Buddhism by banning all Buddhist monks from
Seoul, drastically reducing the power and wealth of the Buddhist hierarchy,
 but later he alleviated his action by building temples and accepting Buddhism by making a test to become a
In the year 1427 Sejong ordered a decree against the Huihui (
Korean Muslim) community that had had special status and
stipends since the
Yuan dynasty. The Huihui were forced to abandon their headgear, to close down their "ceremonial hall" (
Mosque in the city of
Kaesong) and worship like everyone else. No further mention of Muslims exist during the era of the
In relationship with the Chinese
Ming, he made some successful agreements that benefited Korea. In relationship with
Jurchen people, he installed 10 military posts - 4 counties (郡) and 6 garrisons (鎭) - in the northern part of the
He maintained good relations with Japan by opening three ports and allowing trade with them. But he also invaded
Tsushima island with military forces in order to stop pirating in the South Sea (East China Sea) since Tsushima island was a base for pirates.
Strengthening of the Korean military
King Sejong was an effective military planner. He created various military regulations to strengthen the safety of his kingdom,
 supported the advancement of Korean
military technology, including
cannon development. Different kinds of mortars and fire
arrows were tested as well as the use of
In May 1419, King Sejong, under the advice and guidance of his father Taejong, embarked upon the
Gihae Eastern Expedition, the ultimate goal of this military expedition to remove the nuisance of Japanese pirates who had been operating out of
Tsushima Island. During the expedition, 245 Japanese were killed, and another 110 were captured in combat, while 180 Korean soldiers were killed. 146 Chinese and 8 Korean kidnapped were liberated by this expedition. In September 1419 a truce was made and the Korean army returned to Korea, but the
Treaty of Gyehae was signed in 1443, in which the Daimyo of Tsushima promised to pay tribute to the King of Joseon; in return, the Joseon court rewarded the Sō clan with preferential rights regarding trade between Japan and Korea.
In 1433, Sejong sent
Kim Jongseo (
hanja: 金宗瑞), a prominent general, north to destroy the
Jurchens (later known as the
Manchus). Kim's military campaign captured several castles, pushed north, and expanded Korean territory, to the
 4 counties and 6 garrisons (
hanja: 四郡六鎭) were established to safeguard the people from the Jurchen.
Science, Technology, and Agriculture
Sejong is credited with great advances in science during his reign.
 He wanted to help farmers so he decided to create a farmer's handbook. The book—the Nongsa jikseol (
hanja: 農事直說)—contained information about the different farming techniques that he told scientists to gather in different regions of Korea.
 These techniques were needed in order to maintain the newly adopted methods of intensive, continuous cultivation in Korean agriculture.
During his rule,
Jang Yeong-sil (
hanja: 蔣英實) became known as a prominent inventor. Jang was naturally a creative and smart thinker as a young person. However, Jang was at the bottom of the social class. Sejong noticed Jang's skill and immediately called him to his court in Seoul. Upon giving Jang a government position and funding for his inventions, officials protested, believing a person from the lower classes should not rise to power among nobles. Sejong instead believed Jang merited support because of his ability. Jang created new significant designs for
armillary spheres, and
 In 1442, Jang made the world's first
rain gauge named
 it was the idea of Munjong, Sejong's son and heir. This model has not survived, since the oldest existing East Asian rain gauge is one made in 1770, during the reign period of King
Yeongjo. According to the
Daily Records of the Royal Secretariat (
hanja:承政院日記) King Yeongjo wanted to revive the glorious times of King Sejong the Great, and so read chronicles of Sejong's era. When he came across mention of a rain gauge, King Yeongjo ordered a reproduction. Since there is a mark of the
Qing Dynasty ruler
Qianlong (r. 1735–1796) of China, dated 1770,
 this Korean-designed rain gauge is sometimes misunderstood as having been imported from China.
Korean celestial globe first made by the scientist Jang Yeong-Sil during the Chosŏn Dynasty under the reign of
Sejong also wanted to reform the
Korean calendar system, which was at the time based upon the
longitude of the Chinese capital.
 Sejong, for the first time in Korean history, had his astronomers create a calendar with the Joseon capital of
Seoul as the primary meridian.
 This new system allowed Korean astronomers to accurately predict the timing of solar and lunar
In the realm of
traditional Korean medicine, two important treatises were written during the reign of Sejong. These were the Hyangyak jipseongbang and the Euibang yuchwi, which historian Kim Yongsik says represents 'Koreans' efforts to develop their own system of medical knowledge, distinct from that of China.'
Sejong depended on the agricultural produce of Joseon's farmers, so he allowed them to pay more or less tax according to fluctuations of economic prosperity or hard times. Because of this, farmers could worry less about tax quotas and work instead at surviving and selling their crops. Once the palace had a significant surplus of food, King Sejong then distributed food to poor peasants or farmers who needed it. In 1429 Nongsa-jikseol (
hanja: 農事直說, "Explanations of Agriculture") was compiled under the supervision of King Sejong. It was the first book about Korean farming, dealing with agricultural subjects such as planting, harvesting, and soil treatment.
Although most government officials and aristocrats opposed usage of hangul, lower classes embraced it, became literate, and were able to communicate with one another in writing.
Sejong's personal writings are also highly regarded. He composed the famous
Yongbi Eocheon Ga ("Songs of Flying Dragons", 1445), Seokbo Sangjeol ("Episodes from the Life of Buddha", July 1447), Worin Cheon-gang Jigok ("Songs of the Moon Shining on a Thousand Rivers", July 1447), and the reference Dongguk Jeong-un ("Dictionary of Proper Sino-Korean Pronunciation", September 1447).
In 1420 Sejong established the
Hall of Worthies (집현전; 集賢殿; Jiphyeonjeon) at the
Gyeongbokgung Palace. It consisted of scholars selected by the king. The Hall participated in various scholarly endeavors, of which the best known may be the compilation of the
King Sejong the Great profoundly affected Korean history with his personal creation and introduction of
hangul, the native phonetic
alphabet system for the
Before the creation of Hangul, people in Korea (known as
Joseon at the time) primarily wrote using
Classical Chinese alongside native phonetic writing systems that predate Hangul by hundreds of years, including
 However, due to the fundamental differences between the Korean and Chinese languages,
 and the large number of characters needed to be learned, there was much difficulty in learning how to write using Chinese characters for the lower classes, who often didn't have the privilege of
education. To assuage this problem, King Sejong created the unique alphabet known as Hangul to promote literacy among the common people.
 His intention was to establish a cultural identity for Korea through its unique script.
King Sejong presided over the introduction of the 28-letter Korean alphabet, with the explicit goal being that Koreans from all classes would read and write. Each hangul letter is based on a simplified diagram of the patterns made by the human speech organs (the mouth, tongue and teeth) when producing the sound related to the character.
Morphemes are built by writing the characters in syllabic blocks. The blocks of letters are then strung together
The Hangul alphabet was completed in 1443 and published in 1446 along with a 33-page manual titled Hunmin Jeong-um, explaining what the letters are as well as the philosophical theories and motives behind them.
 The Hunmin Jeong-um purported that anyone could learn Hangul in a matter of days. Persons previously unfamiliar with Hangul can typically pronounce Korean script accurately after only a few hours of study.
Death and Legacy
The tomb of Sejong the Great located in Yeoju, Gyeonggi Province, South Korea.
Sejong was blinded years later by diabetes complications that eventually took his life in 1450. He was buried at the
Yeong Mausoleum (영릉; 英陵). His successor was his first son,
Munjong. Sejong judged that his sickly son,
Munjong, was unlikely to live long and on his deathbed asked the
Hall of Worthies scholars to look after his young grandson,
Danjong. As predicted,
Munjong died two years after his accession, and political stability enjoyed under Sejong disintegrated when
Danjong became the sixth king of
Joseon at the age of twelve. Eventually, Sejong's second son,
Sejo, usurped the throne from
Danjong in 1455. When the
six martyred ministers were implicated in a plot to restore
Danjong to throne,
Sejo abolished the Hall of Worthies, and executed
Danjong and several ministers who served during Sejong's reign.
Sejongno and the
Sejong Center for the Performing Arts, both located in central
Seoul, are named after King Sejong.
King Sejong is on the Korean 10,000 won bill, along with the various scientific products made under his reign.
In early 2007, the
Republic of Korea government decided to create a special administrative district from part of the present
Chungcheongnam-do Province, near what is presently
Daejeon. The district will be named
Sejong Special Autonomous City.
The life of Sejong was depicted in the
KBS Korean historical drama
King Sejong the Great in 2008.
 Sejong is also depicted in the 2011
Deep Rooted Tree.