Yi Ja-chun was a mingghan (chief of one thousand) of the Yuan Dynasty in Shuangcheng (雙城; Ssangseong in Korean, now Yŏnghŭng, Hamgyŏngnamdo, North Korea), but his ethnicity was Korean. After Shuangcheng was annexed by Goryeo under King Gongmin, he migrated to Hamju, Hamgyŏngnamdo and got promoted to manho (tümen, chief of ten thousand). He died there in 1360.
Since he was glamorized by his descendants, descriptions of Yi Ja-chun's life are contradictory to each other. For example, he is said to have rose to the rank of scholar-official. However when he died, the king expressed condolences for Jachun as for scholar-officials. That implies that he was not a scholar-official.