태종에 의해 佐命功臣에 책봉된 柳沂는 서산류씨로 고려 말 신흥사대부이며 대학자인 柳淑의 손자로 태어났다. 류숙은 공민왕 때 정치적으로 크게 활약하여 5차례나 공신에 책봉되었으나, 신돈에 의해 죽임을 당하면서 가문의 정치적 위상은 쇠락하였다. 그러나 학문적으로는 과거의 좌주문생제와 원나라에서의 학문적 교유를 기반으로 다양한 인적 네트워크가 형성되었고, 순흥안씨·한산이씨 집안과는 혼맥을 형성하였다. 류숙에 의해 형성된 서산류씨의 인적 네트워크 속에서 류기는 고려 말에 관직에 나아갔고, 조선 건국 정국에서 다채로운 행보를 보였다. 조선이 건국되기 전에 타계한 류기의 큰아버지 류실은 류숙의 과거 문생이었던 정도전과 가까이 지냈으나, 이색의 손녀사위였던 류기는 정도전과 정치적 행보를 함께 할 수 없었다. 그러나 정도전이 제거된 이후에는 이방원을 도와 정치활동을 하기 시작했고, 태종이 즉위한 후에는 좌명삼등공신에 책봉되어 잠시나마 정치적 특권을 누릴 수 있었다. 하지만 태종의 공신정책에 희생양이 된 류기는 이무의 옥사에 연루되면서 謀反大逆罪로 극형에 처해지고, 그의 친족들까지 연좌되어 유배를 당하는 등 한때 가문의 위기가 초래되기도 했다. 한편, 사건이 발생한지 20여 년이 지나자 류기의 죄를 모반대역이 아닌 亂言事로 자리매김한 세종에 의해 류기의 친족들은 연좌죄의 그늘에서 벗어나기 시작했다. 1431년(세종 13)에 류기의 동생 류한은 고신을 돌려받고 벼슬길이 열렸으며, 1455년 (세조 1)에는 류기의 손자들도 과거 응시가 허락되어 仕宦의 길을 걸을 수 있게 되었다. 나아가 1460년(세조 6)에는 류기의 손녀사위가 史官에 제수되고, 1465년(세조 11)에는 류기의 손자가 사헌부 감찰에 제수되기에 이르렀다. 이러한 친족의 연좌죄 탈피에는 류숙에서부터 시작된 집안의 인적 네트워크와 학문적 성과가 크게 작용했다. 그리하여 『신증동국여지승람』 서산군 인물조에는 수록된 5명 가운데 류숙과 그의 자손들이 4명이나 등재되기에 이르렀다.
Ryu Gi, who was invested in Jwamyeong Meritorious Retainers (佐命功臣) by King Taejong (太宗), was one of Seosan Ryu Family and also the grandson of Ryu Suk: the member of the Newly Arisen Scholar Officials (新興士大夫) and great scholar in late Koryo Dynasty. Ryu Suk was politically active and invested as meritorious retainers five times during King Gongmin’s reign. However, after Ryu Suk got killed by Shin Don, Ryu Family’s political status declined. Still, Ryu Family made various informal academic networks through Jwajumunsaengjeh (座主門生制)-a custom of teaching relationship between examiners and successful candidates-and through academical and social communication in Yuan. They especially made networks with Sunhung Aan Family and Hansan Lee Family through marriage. Thanks to Seosan Ryu Family’s informal networks made by Ryu Suk, Ryu Gi was able to become an official in late Koryo Dynasty, showing various actions in the process of establishing Josun Dynasty. Ryu Gi’s uncle Ryu Sil who had passed away before the establishment of Josun, had friendly relationship with Jong Dojon who was once Ryu Suk’s student. However, Ryu Gi couldn’t take political actions with Jong Dojon because he was Lee Saek’s granddaughter’s husband. Fortunately, after Jong Dojon was eliminated, he started to act with Lee Bangwon. As a result, he was invested in 3rd place of Jwamyeong Meritorious Retainers, earning temporary privilege politically soon as King Taejong was crowned. Unfortunately, Ryu Gi became a scapegoat of King Taejong’s Purge. Because he was indirectly involved in Lee Mu’s imprisonment, Ryu Gi himself was executed for a treason felony (謀反大逆罪) as his family took its responsibility and got exiled. 20 years after the incident, King Sejong resolved Ryu Gi’s crime as ‘unintentional words’ instead of treason felony. As a result, Ryu Gi’s family started to take off their offense. In 1431 (Sejong’s 13th year o freign), Ryu Han (Ryu Gi’s younger brother) got his appointment letter-Gosin (告身)-back and was able to become officials again. In 1455 (King Sejo’s 1st year of reign), Ryu Gi’s grandsons were able to take Gwageo examination. Further more, in 1460 (Sejo’s 6th year of reign), Ryu Gi’s granddaughter’s husband was invested as history compiler, by King Sejo directly. In 1465 (King Sejo’s 11th year of reign), even Ryu Gi’s grandson was invested as an inspector of Saheonbu (司憲府). Ryu Family’s informal network and academic results started from Ryu Suk gave a huge effect on the process of taking off their offense. As a result, In the book Shinjung donguk yeoji sungnam (新增東國輿地勝覽), the chapter of Seosan, Ryu Suk and his descendants were chosen as 4 out of 5 important people.