Jin Dajian was a craftsman from Jizhou, and a good friend of Wu Yong. He was an excellent sculptor who could carve stone tablets, official seals etc. He was also good in martial arts as well and due to excellent skills in carving jade rocks, he was nicknamed the 'Jade-armed Craftsman' (玉臂匠).
Once, Song Jiang wrote a poem which defamed the government and was thrown into prison. Dai Zong went to Jizhou to trick Xiao Rang and Jin Dajian to Liangshan under Wu Yong's instruction. Xiao Rang forged a letter from Cai Jing, telling the governor of Jiangzhou to have Song Jiang escorted to the capital city, while Jin Da-jian completed the picture by adding a fake seal on the letter which he carved.