An Daoquan was from Jiankangfu, and inherited medical skills passed down by his ancestors. He became a reowned physician and could treat all kinds of illnesses, thus he was nicknamed 'Holy Physician' (神医).
When Song Jiang led the Liangshan heroes to attack Damingfu, he contracted a growth on his back and was forced to abandon the offensive and retreat back to Liangshan. Zhang Shun's mother had suffered from a similar illness as Song Jiang before, and was treated by An Daoquan. So, Zhang recommended An Daoquan to treat Song Jiang.