Military officer who developed the Jeongcheol chongtong (matchlock) under Yi Sun-sin in the Imjin War, pen name Seongeun, mid-founder of the Seongeun-gong branch
| Life | 1553 |
| Era | 조선 중기 |
| Clan | 경주 정씨 |
Jeong Sa-jun, courtesy name Geun-cho and pen name Seongeun, was a native of Suncheon in Jeolla Province and a son of Jeong Seung-bok; one clan source says the third son. He passed the 1584 special military examination in the upper class, and in the Imjin War served as Hunryeon jubu under Yi Sun-sin.
His best-known deed is developing the Jeongcheol chongtong, a firearm modeled on the Japanese matchlock. The Suncheon encyclopedia says Yi Sun-sin submitted reports three times about the military merit of Jeong Sa-jun and his brothers. A clan cafe post adds that he served as an ambush commander in the Gwangyang Bay fighting and donated grain on hearing of food shortages at Uiju; as this comes from a single source, it is best taken as tradition.
He is said to have been impeached for greed and dismissed while magistrate of Gyeolseong in 1599, and was posthumously raised to Vice Minister of War.
The Jeongcheol chongtong is known as a Joseon firearm modeled on the Japanese matchlock. Jeong Sa-jun is said to have made it, but sources describing its structure and the course of its manufacture were not confirmed. It is cited as an example of effort by a provincial officer in the process by which Joseon took up the matchlock.
Clan materials describe Jeong Sa-jun as mid-founder of the Seongeun-gong branch and name Jeong Sun, Jeong Bin and Jeong Yeol among its members. One account counts Jeong Seung-bok as 54th and Jeong Sa-jun as 55th generation from the 46th-generation Hyeon-yeong of the Munheon-gong branch. Generation numbers vary by source and should be checked against the register.
A spirit-path stele is said to stand at Dongsan-ri, Seo-myeon, Suncheon.
His son Jeong Seon (courtesy name Gwanjung) passed the military examination, became a royal escort and accompanied King Seonjo on his flight to Uiju. His younger brothers Jeong Sa-hoeng, Jeong Sa-rip and Jeong Sa-jeong served with Yi Sun-sin, and his nephew Jeong Bin is said to have gathered army grain for Uiju. His descendants form the Seongeun-gong branch, honored him as mid-founder within the Okgye-gong line of Jeong Seung-bok.