Who is Hawk in the novel, Early Autumn?

Hawk is the black man who Spenser described as being almost as good at protecting clients and fighting as Spencer is. It's Hawk Spenser calls on when the kidnappers have Patty and want to trade her for Paul. Hawk and Spenser are actually pitting their skills at the fast bag at Henry Cimoli's gym when Hawk is called to the phone. He returns, telling Spenser that Harry Cotton had tried to hire him to kill Spenser. Hawk's ability to defend himself makes him unwilling to run from any fight, and he says he wants to stick with Spenser for awhile on the chance that someone else will prompt a fight. When Cotton sends another gunman to kill Spenser and Susan is put in danger, Hawk goes with Spenser to put a stop to the attacks. When Spenser refuses to kill Cotton, saying that he can't shoot a man who is lying on the floor, Hawk says he has no such compunction and kills Cotton.