Sixkill by Robert B. Parker

Sixkill (Spenser Mystery) - Spenser is asked by Quirk to investigate the death of a young girl who died while having sex with movie star Jumbo Nelson.  When Spenser talks with the Nelson, Nelson orders his bodyguard, Zebulon Sixkill to eject Spenser.  Spenser makes short work of Sixkill and Nelson fires Sixkill.  Later, Spenser finds Sixkill laying drunk at his office doorstep.  Spenser takes him in and begins to train him.