| Yi Cha-ch'un 이자춘 李子春 | |
| King of Joseon (posthumously) | |
| Succession: | Darugachi |
| Reign: | 1343–1356 |
| Birth Date: | 20 January 1315 |
| Birth Place: | Aldong, Ssangseong Prefecture, Yuan dynasty (now Gyeongheung-gun, North Hamgyeong Province) |
| Death Date: | 3 June 1361 (aged 46) |
| Death Place: | Gwiju-dong, Hamheung-bu, Dongbuk-myeon, Goryeo (now Yeongheung-gun, Hamgyeongnam-do) |
| Burial Place: | Jeongneung tomb Hamju County, South Hamgyeong Province, North Korea |
| Spouse: | Lady Yi Queen Uihye |
| Issue: | 5 sons and 1 daughter |
| Posthumous Name: |
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| Temple Name: | Hwanjo (환조, 桓祖) |
| House: | Jeonju Yi |
| Father: | Yi Chun |
| Mother: | Lady Bak of the Munju Bak clan |
Yi Cha-ch'un (; 20 January 1315 – 3 June 1361) or known by his Mongolian name Ulus Bukha, 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 Cha-ch'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. ten thousand or chief of ten thousand). He married a Goryeo-Korean lady from Anbyeon, who became Queen Uihye, the mother of Yi Sŏng-gye. He died in Hamgyong in 1361.
Since he was glamorized by his descendants, descriptions of Yi Cha-ch'un'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 Cha-ch'un as if for scholar-officials, implying that Yi Cha-ch'un was not a scholar-official.