Yi Chach'un (Korean: 이자춘; Hanja: 李子春; 20 January 1315 – 3 June 1361) or known by his Mongolian name Ulus Bukha (Korean: 울루스부카; Hanja: 吾魯思不花), was a minor military officer of the Yuan Empire who later transferred his allegiance to Goryeo and became the father of Yi Sŏng-gye, founder of the Joseon Dynasty.
Yi Chach'un was a chiliarch of a Yuan Dynasty mingghan in Ssangseong Prefecture (present-day Kŭmya County, South Hamgyŏng Province, North Korea - former Goryeo territory annexed by Mongol Empire).
After Ssangseong was reconquered by Goryeo under King Gongmin, he migrated to Hamju and got promoted to manho (the equivalent of the Mongolian myriarch of a tümen, lit.
He married a Goryeo-Korean lady from Anbyeon, who became Queen Uihye, the mother of Yi Sŏng-gye.
Since he was glamorized by his descendants, descriptions of Yi Chach'un's life tend to be contradictory to each other.