Who is Leonard from A Million Little Pieces and what is their importance?

Leonard is a west-coast mafioso addicted to cocaine. He is very wealthy, extremely generous, supportive, and firm, and becomes something of a father figure for James while they are both at the Clinic. When James tries to walk out of the Clinic, Leonard stops him and convinces him to stay long enough to get healthy. He also exerts some influence with the court system in order to have James's prison sentence reduced.