Yi Ja-chun (Mongolian name: Ulus Bukha ; 1315 – 1361) was a minor military officer of the Yuan Dynasty (he later transferred allegiance to the Goryeo Dynasty) and the father of Yi Seong-gye, the founder of the Joseon Dynasty. He was given the temple name Hwanjo (; ) by Taejong.
Yi Ja-chun was a mingghan (chief of one thousand) of the Yuan Dynasty in Ssangseong Prefectures (; Ssangseong in Korean, now Y?ngh?ng, Hamgy?ngnamdo, North Korea - territory which was then administered by the Mongol Empire as part of the terms of the vassaldom of Goryeo to that empire),  After Ssangseong was annexed by Goryeo under King Gongmin, he migrated to Hamju, Hamgy?ngnamdo and got promoted to manho (the equivalent of the Mongolian tümen, lit. ten thousand or chief of ten thousand). He married a Chinese lady from Shandong, who became Queen Uihye, the mother of Yi Taejo. He died in Hamgyong in 1361.
Since he was glamorized by his descendants, descriptions of Yi Ja-chun's life tend to be contradictory to each other. For example, he is said to have risen to the rank of scholar-official. However, when he died, the king at the time expressed condolences for Jachun as if for scholar-officials, implying that Yi Ja-chun was not a scholar-official.