One of the Three Eun of late Goryeo and root of the Joseon Sarim scholarly line; pen names Yaeun and Geumosanin; posthumous title Chungjeol

| Life | 1353 ~ 1419 |
| Era | 고려 말~조선 초 |
| Clan | 해평 길씨 |
Gil Jae (1353-1419) was a Neo-Confucian scholar of the late Goryeo and early Joseon periods from the Haepyeong Gil clan, with courtesy name Jaebo and pen names Yaeun and Geumosanin. The clan honors him, together with his father Gil Won-jin, as its mid-founder. He is said to have studied under Yi Saek, Jeong Mong-ju and Gwon Geun, although whether he was a direct pupil of Jeong Mong-ju is disputed.
He passed the licentiate examination in 1374 and the civil examination in 1386, then served as Erudite of the Seonggyungwan and Secretary of the Chancellery. Seeing Goryeo in decline, he resigned to care for his aged mother and returned to his home in Seonsan; after Joseon was founded in 1392 he still refused office. In 1400 Yi Bang-won (later King Taejong) offered him the post of Taesang Baksa, which he is said to have declined, saying he could not serve two dynasties.
He taught students at home, and his teaching passed through Kim Suk-ja to Kim Jong-jik, Kim Goeng-pil, Jeong Yeo-chang and Jo Gwang-jo, making him regarded as the root of the Joseon Sarim school. He died in 1419 and is said to have received the posthumous title Chungjeol under King Yeongjo. His collected works, the Yaeun-jip, survive, and his sijo poem on the old capital is widely known.
He is said to have learned to read at a temple and then studied Neo-Confucianism in Gaegyeong under Yi Saek, Jeong Mong-ju and Gwon Geun. He passed the licentiate examination in 1374 and the civil examination in 1386, and in 1388 became Erudite of the Seonggyungwan.
He became Secretary of the Chancellery in 1389 but soon resigned, citing his mother's care, and returned home. When Yi Bang-won offered the post of Taesang Baksa after the founding of Joseon, he declined on the principle that a loyal subject does not serve two kings; an anecdote says he also refused gifts of rice and beans, though such stories vary by source.
His teaching passed to Kim Suk-ja, whose son Kim Jong-jik carried it on to Kim Goeng-pil, Jeong Yeo-chang and Jo Gwang-jo, which is why he is seen as the root of the Sarim faction. He is also said to have been listed as a model of loyalty in the 1431 Samgang haengsildo. A tale says King Sejong allowed his descendants to hold office, but accounts differ.
Below Mt. Geumo in Gumi stand Geumo Seowon (Gyeongsangbuk-do Monument No. 60) and Chaemijeong pavilion (Scenic Site No. 52) in his memory. Geumo Seowon was founded around 1570 at the Confucian community's request and, after burning in the Imjin War, rebuilt on its present site in 1609; its royal charter is dated 1575 or 1669 depending on the source. Chaemijeong was built in 1768 by Seonsan magistrate Min Baek-jong and is said to take its name from the story of Boyi and Shuqi.
His tomb is said to lie in Otae-dong, Gumi, at the foot of Mt. Geumo. A report suggests the stele before it dates to 1725, but this is not firmly established.
His sons are said to include Gil Sa-mun and Gil Sa-sun, and his daughters married into the Kim, Yi and Han families. Some descendants are said to have settled around Buri and Nami in Geumsan, South Chungcheong.