Who is Lu Da from Water Margin and what is their importance?

Lu Da is a major in the garrison, whom Shi Jin meets in a tea house in Weizhou. Lu takes charge of Lotus and her father by ensuring that the innkeeper will let the father and daughter go. He then accidently beats Master Zheng to death and escapes to Yanmen. Old Jin, who is Lotus' father, arranges for his daughter's new husband, Squire Zhao, to set Lu Da up with an appointment in a monastery. He is passed off as a cousin of Squire Zhao. During his time at the monastery Lu Da is called Sagacious Lu the Tattooed Monk.