Zhu Fu was the younger brother of Zhu Gui, and he ran a restaurant. He learnt martial arts from Li Yun and was one of Li's favourite students. He was nicknamed 'Smiling tiger' (笑面虎).
Once, Zhu Gui was put in charge of looking out for Li Kui, who had gone home to fetch his mother to Liangshan, as Song Jiang was worried that Li Kui might run into trouble. As expected that he would run into some trouble, Li Kui was made drunk by Lord Cao and captured after he killed the imposter Li Gui and the four tigers which devoured his mother. Li Yun, a constable at that time, was assigned to escort Li Kui as a prisoner to the county office.