Introduction
Yu Sang (Korean: 유상; Hanja: 柳瑺; 柳尙; 柳相; 1643–1723), alternatively Ryu Sang (Korean: 류상), courtesy name Yeojin (汝珍, 여진), was a royal court physician and politician of the Korean Joseon dynasty. He was a smallpox specialist who successfully treated three Joseon kings.
In 1693, due to having cured Sukjong's smallpox, he was granted a political office. Later he became the governor of Seosan, Goyang, Hapcheon and Saknyeong.
His experiences with smallpox are detailed in his book, Gogeum Gyeongheom Hwalyubang (古今經驗活幼方).
Supernatural anecdotes featuring him and a divine being circulated due to his fame.
Family
He was a 23rd-generation descendant of the Munhwa Ryu clan. His father Yu Gyeongjib (柳景緝) served as an observation officer (觀察使, gwanchalsa). His son Yu Jungrim (柳重臨) was also a medical practitioner who also wrote the agricultural text Jeungbo sallim gyeongje.