Kim Chung-seon (1571–1642) born Sayaka (沙也可) and often known by his pen name Mohadang, was a Japanese general who defected to Korea during the Japanese invasion. However there is no proof a person by this name ever existed in Japan. More importantly the name "Sayaka" could not be a samurai name. Some theories suggest Sayaka to be a Korean misinterpretation of Saika, referring to the Saika Shu. This once again has no historical basis, and is simply based on the similarity of names. An important note is that the Saika Shu were commanded to remain at Nagoya Castle by Hideyoshi and never entered Korea.
Kim Chung-seon is said to have been the commander of the right army for Katō Kiyomasa, leading more than 3,000 troops. He defected shortly after arriving on Korean soil, surrendering to Gyeongsang commander Pak Jin. This choice has been traditionally attributed to his respect for Korean culture. This has not been confirmed, as there is no record of a Sayaga or Sayaka within the available documentation regarding Kiyomasa's troops.
After his defection, Kim served in the Joseon army, contributing to Korean victories over Japanese forces in the battles of Dongnae and Ulsan. Thereafter he was granted his Korean name, on the recommendations of Gwon Yul and others, and was made part of the Gimhae Kim lineage.
Kim continued his military service after the end of the Japanese invasions in 1598, working for 10 years on securing the northern border. He fought the rebellion of Yi Gwal in 1624, personally capturing Yi's lieutenant Seo A-ji (서아지 / 徐牙之). In 1636, he participated in the defense against the Second Manchu invasion of Korea, credited with the death of some 500 Qing troops at the battle of Ssangnyeong.
After Joseon's surrender to the Manchus, Kim retired from military life, moving to Daegu where he married the daughter of the mok commander Jang Chun-jeom (장춘점 / 張春點). They settled in present-day Urok-ri, Gachang-myeon, Dalseong-gun. Kim devoted himself to Confucian ethics, promulgating gahun (family principles) and hyangyak (village creed).
The Nokdong Seowon in Urok-ri was erected in his memory in 1789. This seowon was abolished in 1864 as part of the regent Daewon-gun's general campaign against seowon, but was reestablished in 1914 under the Japanese colonial regime. The seowon remains a popular destination for Japanese tourists in Daegu.
Kim's 6th-generation descendants compiled his collected works, which exist in two editions.