Sullivan is Mendelson's chief henchman and a fellow member of the New Confederates, a white supremacist gang during House's stay in East New Jersey Correctional Facility, the prison House is sent to in the Season 8 episode Twenty Vicodin. He was portrayed by actor Michael Bailey Smith.
Sullivan acts as Mendelson's messenger and muscle. At well over six feet tall and close to 250 pounds, he works mostly by intimidation rather than overt physical violence. Although he's much younger and bigger than Mendelson, he's afraid to challenge him openly.
When Mendelson decides to make an example of House, he orders Sullivan to stab House. Sullivan resists and we learn for the first time that, like House, he is concerned about behaving himself so he can get out of prison as soon as possible. However, when Mendelson presses the matter, he agrees. However, as he goes to stab House, he's attacked from behind by Curtis Asofa and knocked unconscious.