Christopher 'Sully' Sullivan (portrayed by Matt Barr) is Henry's best man. All of his friends call him Sully, and he has lots of friends. He's a fun-loving frat boy at heart whose good buddies live vicariously through his many sexual escapades. He's been Henry's best friend since high school, but it's questionable if he's at the wedding more for Henry's benefit or for the bachelor party and bridesmaids, particularly when he gets an eyeful of Chloe.
In "Crackle", Sully discovers Cal cought in a snare trap and promises he'll bring help, but after the party begins, he forgets and accidently leaves Cal hanging upside down overnight. When Cal is discovered and saved, Sully tries to apologize to little success. Cal finally gets his revenge in the next episode when he has Chloe, his girlfriend, pretend to hit on Sully and take him to a massage booth. While there, she has him lathered in honey, and then Cal arrives and dumps a pillow full of feathers on him. Now even, the two begin to become friends.
Sully, along with Malcolm, Danny, and Booth, becomes paranoid that drug dealers are after them when they discover Marty Dunn's suitcase of money in Hunter Jennings' boat. He calms down after discovering that the supposed "drug dealers" are simply the bouncers for the stripper that Sully has hired for Henry's bachelor party.
Sully helps as much as he can to survive with the rest of the group after Thomas Wellington is killed in Episode 5, revealing to everyone that a killer is on the loose. In Episode 7, Malcolm confesses to him and Danny that he accidently got Booth killed in a situation involving the money.
In Episode 8, Sully and several other characters decide to leave the island despite the killer (John Wakefield) saying Madison will die if anyone tries to leave. They eventually decide to stay due to complications.
Sully becomes mistrustful of Abby after evidence surfaces that she is the child of John Wakefield.
In Episode 10, Cal and Sully are sent on a mission to try and get a boat (Sully gives Nikki a kiss before leaving, implying they had a thing for each other). While running to the car, Cal is shot through the shoulder. Cal almost bleeds out, but is saved by Sully when he manages to patch up the wound. The two eventually discover that there is no boat, much to both of their despair.
Sully is visibly distraught when he sees the corpses of Cal and Chloe floating in the water in Episode 11.
In "Gasp", he and Danny hatch a plan to capture Wakefield. Danny agrees to be used as bait. As Wakefield is sneaking up on him, Sully appears and shoots the killer in the ear. Despite Sully's protests that he should be killed, Abby instead knocks out Wakefield and locks him in the police station.
Sully, Trish and Henry try to get contact with the coast guard through the radio, and finally succeed. Shea tells Sully that Danny has been killed by Wakefield, who escaped from the police station. This causes him to almost break down in tears.
In the finale, Sully, Shea and Madison discover a small lifeboat. As Shea and Madison get in, Sully refuses to come. He tells the two that he wants to stay to help his remaining friends. Shea initially protests, but Sully tells her that Madison is her top priority. Following this, she and Madison leave on the boat.
Sully returns to the boat house with Henry, who, unbeknownst to him, is one of the killers. The coast guard instructs the two to meet them at the marina. While talking to the guard on the radio, Sully doesn't see Henry take his rifle and remove the bullets from it.
DeathEditSully and Henry are heading for the marina when Henry begins to act suspicious, ranting about how Wakefield's son (him) is justified in his anger. He then reveals to Sully that he murdered Trish, and begins listing his various murders as well as the fact that he intentionally placed the money in Hunter's boat to see what would happen when Malcolm inevitably found it. Sully finally snaps and pulls out his gun to shoot Henry, but discovers to his horror that the bullets have been removed.
Henry tells Sully that Wakefield is right behind him. Sully asks how stupid does Henry think he is, and Wakefield reveals himself, saying, "Pretty stupid." This distracts Sully enough for Henry to grab him and stab him in the back with his pocket knife. Henry whispers "You should have never dogged Trish" to him, before ripping the knife out of his back, killing him.
- Sully is one of several characters to appear in all thirteen episodes.
- Sully is the last non-villain death, his demise being followed by that of Wakefield and Henry.
- He is also the last of the wedding guests to die.
- He is shown to be a gamer, for when asked by Trish if he knows how to shoot a gun, Sully repsonds by saying he did it in Halo, Bioshock, and Grand Theft Auto, all of them being video games.