Who is Ken Holloway from The Last Child and what is their importance?

Ken Holloway is the drug addict, who moves in with Johnny's mothee. He supplies her with drugs, and they use them together. His presence in the Merrimon household is one of the reasons Johnny is stays away from home. He regularly beats Katherine until she is bloody and bruised. "The man was a predator, pure and simple," is how the narrator describes him.