He personally created and promulgated the Korean alphabet,[3][4] 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.

"[d] Taejong judged his second son, Grand Prince Hyoryeong, to have a disposition too soft for the role, and would be unable to drink with emissaries from Ming dynasty to entertain them.

However, Taejong retained military power and continued to make major political decisions as king emeritus (상왕; 上王) until his death.

[16] Perpetually wary of royal authority falling into the thrall of the queen's clan, Taejong had Sejong's father-in-law, Shim On, executed on charges of treason.

[17] Despite inheriting significantly strengthened royal authority, Sejong did not suppress the press and promoted meritocracy through gwageo, the national civil service exam.

[citation needed] Likewise, Sejong continued Joseon's policies of "worshiping Confucianism and suppressing Buddhism" (Korean: 숭유억불; Hanja: 崇儒抑佛).

[18] He banned monks from entering Hanseong and reduced the seven schools of Buddhism down to two, Seon and Gyo, drastically decreasing the power and wealth of the religious leaders.

[24] 上謂承政院曰 孟子言 '墨子以薄爲道, 而葬其親厚'。大抵臣子之道, 宜以直事上, 不可容其詐。 然世人在家, 奉佛事神, 靡所不至, 及對人, 反以神佛爲非, 予甚惡之。 The King spoke to the Seungjeongwon, Mencius once said, 'Mozi regards austerity as a virtue and yet made a lavish burial for his parents.'

In 1427, Sejong issued a decree against the Huihui (Korean Muslim) community that had enjoyed special status and stipends since the Yuan dynasty's rule over Goryeo.

[26] In the early years of the Joseon dynasty, the economy operated on a barter system, with cloth, grain, and cotton being the most common forms of currency.

In 1423, under King Sejong's administration, the government attempted to introduce a national currency modeled after the Tang dynasty's kaiyuan tongbao (開元通寶).

[27] In 1445, Sejong consolidated the various sujoji[e] records, previously managed by various government offices, and placed them under the administration of the Ministry of Taxation (Hojo) to improve transparency in Joseon's fiscal policies.

Hand cannons, known as Wangu (완구; 碗口), first built in 1407 and 1418, were improved upon,[30] and the Sohwapo (소화포; 小火砲), Cheoljetanhwan (철제탄환), Hwapojeon (화포전; 火砲箭) and the Hwacho (화초; 火硝) were invented during his reign.

The Chongtongdeungnok (총통등록; 銃筒謄錄) compiled and published in the 30th year his reign, was an illustrated book that described the casting methods, gunpowder usage, and specifications of the guns.

In this agreement, known as the Treaty of Gyehae, the daimyo of Tsushima was obliged to pay tribute to the Joseon monarch, and in return, the Sō clan was allowed to serve as a diplomatic intermediary between Korea and Japan, as well as retain exclusive trade rights.

The Hall of Worthies was designed to host Joseon's best and brightest thinkers, with the government offering grants and scholarships to encourage young scholars to attend.

According to the Daily Records of the Royal Secretariat (승정원일기; 承政院日記; Seungjeongwon Ilgi), Yeongjo wanted to revive the glorious times of Sejong the Great, and started reading chronicles from that era.

These were the Hyangyak Jipseongbang (향약집성방; 鄕藥集成方) and the Euibang Yuchwi (의방유취; 醫方類聚), which historian Kim Yong-sik says represents "the Koreans' efforts to develop their own system of medical knowledge, distinct from that of China".

[46] In order to provide equality and fairness in taxation for the common people, Sejong issued a royal decree to administer a nationwide public opinion poll regarding a new tax system called Gongbeop in 1430.

[47][48] Joseon's economy depended on the agricultural output of the farmers, so Sejong allowed them to pay more or less tax according to the fluctuations of economic prosperity and hard times.

Sejong's independent musical compositions include the Chongdaeop ('Great Achievements'), Potaepyeong ('Preservation of Peace'), Pongnaeui ('Phoenix'), and Yominrak ('A Joy to Share with the People').

The Pyeongyeong is a percussion instrument consisting of two rows of 8 pumice slabs hung on a decorative wooden frame with a 16-tone range and struck with an ox horn mallet.

[52] King Sejong profoundly affected Korea's history with the creation and introduction of hangul, the native phonetic writing system for the Korean language.

[61] King Sejong faced backlash from the noble class as many disapproved of the idea of a common writing system, with some openly opposing its creation.

[64] Its spread and preservation can be largely attributed to three main factors: books published for women, its use by Buddhist monks,[65] and the introduction of Christianity in Korea in 1602.

[67][68] Sejong suffered from eye diseases and deteriorating vision and likely had health issues linked to excessive meat consumption all throughout his life.

[74] As predicted, Munjong died two years after his ascension, and the political stability enjoyed in the past decades disintegrated when Danjong became the sixth king of Joseon at the age of 12.

When six court officials were implicated in a plot to restore his nephew, Sejo abolished the Hall of Worthies and executed Danjong along with several ministers who served during Sejong's reign.

]; while they had numerous children together, and there is evidence of the two caring for and treating each other respectfully, Taejong had the queen's father executed, and Sejong dutifully consented to this.