Central ancestor of the Seongju Yi, whose five sons all passed the civil examination; lived under King Gojong of Goryeo

| Era | 고려 |
| Clan | 성주 이씨 |
Yi Jang-gyeong (李長庚) is the central ancestor of the Seongju Yi and lived under King Gojong of Goryeo. His dates are not recorded. He is said to have been a 12th-generation descendant of the late-Silla minister Yi Sun-yu and a son of Yi Deuk-hui (李得禧), born in Seongju (then Gyeongsan). Wikipedia describes him as a local magnate of Seongju who served as sang-hojang and anil-hojang, local headman posts.
Some traditions surround his name. His father Yi Deuk-hui is said to have dreamed of the Munchang star falling on Gyeongsan, and so named the son Janggyeong (長庚), another name of the Munchang and Taebaek stars. The Seongju magistrate Yi Yak (李若) of the Hapcheon Yi is also said to have recognized his talent and married him to his daughter, who bore the five sons. Both the clan and Wikipedia tell these stories, but they have a legendary tone and should be read apart from fact.
The five sons were Yi Baek-nyeon (Miljik-sasa), Yi Cheon-nyeon (Chamji-jeongsa), Yi Man-nyeon (Munha-sijung), Yi Eok-nyeon (governor of Gaeseong) and Yi Jo-nyeon (Jeongdang-munhak), and all passed the civil examination. As they rose the Goryeo court posthumously gave their father titles such as Samjung-daegwang Munha-jwasijung and Lord of Heungan, and when his grandson Yi Seung-gyeong made a name in Yuan China the Yuan court again granted him the title Duke of Nongseo, after which the house was also called the Nongseo Yi.
The house rose greatly because all five sons passed the civil examination. Wikipedia's Seongju Yi entry lists Yi Baek-nyeon as Miljik-sasa, Yi Cheon-nyeon as Chamji-jeongsa, Yi Man-nyeon as Munha-sijung, Yi Eok-nyeon as governor of Gaeseong and Yi Jo-nyeon as Jeongdang-munhak, though other sources such as Namuwiki write some titles differently. A daughter is said to have married Yi Chang-gan. The clan counts 18 Daejehak, 15 chief ministers and 75 civil-examination graduates within eight generations of him.
His tomb is said to have stood originally on Seonseoksan in Inchon-ri, Wolhang-myeon. When this site was chosen under King Sejong for the placenta chambers of the princes, Wikipedia says Sejong ordered a good site to be found and the tomb moved, and a local newspaper column gives the year as 1443 and the new place as Neunggol in Okhwa-ri, Daega-myeon. The Placenta Chambers of King Sejong's Sons now stand in Wolhang, Seongju. The memorial hall Ohyeonjae beside the tomb is said to honor the founding ancestor Yi Sun-yu and Yi Jang-gyeong together.
He was first buried on Seonseoksan in Inchon-ri, Wolhang-myeon, Seongju, but when a placenta chamber for King Sejong's sons was placed there the tomb was moved in 1443 to Neunggol in Okhwa-ri, Daega-myeon. The nearby memorial hall Ohyeonjae honors him together with the founding ancestor Yi Sun-yu.
His five sons founded the Miljik-gong, Chamji-gong, Sijung-gong, Yusu-gong and Munyeol-gong branches; the line continued through his grandson Yi Seung-gyeong, who passed the Yuan examination, Yi Jo-nyeon's grandsons Yi In-bok and Yi In-im, and his great-grandson Yi Je.