King Taejong, the third ruler of the Joseon Dynasty, reigned from 1400 to 1418 and was a pivotal figure in Korean history. He was the fifth son of King Taejo, the dynasty's founder, and the father of Sejong the Great. Taejong implemented significant military, administrative, and legal reforms. One of his first actions as king was to abolish private armies held by aristocrats, consolidating military power under the central government. This move curbed the potential for large-scale revolts by the upper class and bolstered the national army.

He also revised land taxation laws, leading to increased national wealth by uncovering previously hidden land. Taejong established a strong central government, replacing the Dopyeong Assembly with the State Council. He decreed that all decisions by the State Council required the king's approval, thus centralizing royal authority. Taejong created the Sinmun Office to address grievances against officials or aristocrats and placed a large drum outside the palace for commoners to request an audience for important matters. Taejong promoted Confucianism over Buddhism, leading to the decline of the latter's influence and the closure of many temples.

His foreign policy was aggressive, attacking Jurchens in the north and Japanese pirates in the south. Taejong initiated the Ōei Invasion of Tsushima Island in 1419. He introduced the hopae system, an early form of identification, to control population movement. Taejong advanced metal movable type printing technology, ordering the creation of 100,000 pieces of metal type and two complete fonts, predating Gutenberg. He encouraged publications, commerce, education, and granted independence to the Uigeumbu, a judicial body.

In 1418, Taejong abdicated in favor of his son Yi Do (Sejong the Great) but continued to exert influence over state affairs. He executed or exiled supporters who helped him ascend to the throne and limited the influence of in-laws and powerful clans, including executing the brothers of his wife, Queen Wongyeong. Taejong died in 1422 at Sugang Palace and was buried with Queen Wongyeong at Heonneung in Seoul. His reign, marked by effective governance and harsh measures against rivals, significantly contributed to Joseon's stability and prosperity, setting a firm foundation for his successor's successful reign.