Gavin is a minor character from I Work For A Monster that was introduced in Brad's journal entries. He used to work with Brad as a fellow hitman for Jessica Carter's criminal empire until he orchestrated a failed coup.
After Brad saves a little girl who was kidnapped by Jessica Carter, he went to Gavin for help. He noticed that Gavin seemed distracted the entire time, a strange occurence he blamed on a mysterious woman with red eyes that had been following him lately. Brad assumed that this strange woman was Gavin's ex-girlfriend at first, so he didn't pay too much attention to it at the time despite his irritation over her frequent appearances. However, after the little girl mentions seeing a mysterious dog scratching at her window during the night, Gavin admitted that he had been stalked by The Black Dog for over a year now and that the red-eyed woman was simply another form it takes from time to time. Gavin is convinced that the Dog is going to kill him soon, so he suggests an elaborate scheme in which they lure the Black Dog to a specific location where it will "assassinate" Jessica to Brad.
Brad dismisses this story as complete nonsense, only for him to realize that the Black Dog is very real when he sees it for himself. They decide to go through with Gavin's plan, but it fails spectacularly due to the Black Dog's instinct to ignore Jessica whenever it encounters her, a fact neither one of them was aware of. Gavin's fate after his betrayal is not touched upon in the story, though he was most likely killed by the Black Dog or Jessica.