He was a member of the Yeon clan (燕氏), one of the "Great Eight Families" (Daeseongpaljok, 大姓八族).
[3] Since he was not fit to oversee the military, the armies continued to be overseen by General Hae Gu, who maintained actual political control.
In January, 478, Hae Gu made common cause with rebels based in Daedu Fortress led by Yeon Sin.
Samgeun first sent the noble, the Sahei (佐平: 1st official rank) Jin Nam to capture the castle with 2,000 men, but he failed.
He then sent the Dalsol (德率: 4th official rank) Jin Ro, who defeated the rebels with 500 men, whereupon Yeon Sin fled to Goguryeo.