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. 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 Chach'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 Chach'un as if for scholar-officials, implying that Yi Chach'un was not a scholar-official.^{[citation needed]}

• Father: Yi Ch'un (1265–1342)
  • Grandfather: Yi Haeng-ni (1236–?)
  • Grandmother: Queen Jeongsuk of the Deungju Ch'oe clan (1232–?)
• Mother: Queen Gyeongsun of the Munju Pak clan (1268–?)
  • Grandfather: Pak Kwang (박광; 1240–?)
• Wives and their Children:

1. Queen Uihye of the Yeongheung Ch'oe clan (의혜왕후 영흥 최씨; 1304–?)
   1. Princess Jeonghwa (1330–?), First daughter
   2. Yi Sŏng-gye, King Taejo of Joseon (1335–1408), Third son
2. Royal Noble Consort Yi of the Hansan Yi clan (빈 한산 이씨; 1319–1334)
   1. Yi Wŏn-gye, Grand Prince Wanpung (1330–1388), first son
   2. Yi Cheon-gye, Grand Prince Yeongseong (1333–1376), second son
3. Royal Noble Consort Jeong, of the Gim clan (정빈 김씨; 1320–1404)
   1. Yi Hwa, Grand Prince Uian (1348–1408), Fifth son
4. Unknown woman (1325–?)
   1. Yi Yŏng (이영; 1341–1394), Fourth son

• Portrayed by Jeon Byung-ok in the 2005–2006 MBC TV series Shin Don.
• Portrayed by Jung Dong-gyu in the 2012 SBS TV series Faith.
• Portrayed by Lee Soon-jae in the 2015–2016 SBS TV series Six Flying Dragons.

• List of Goryeo people
• History of Korea