Gordon Walker, portrayed by Sterling K. Brown, is a vampire hunter whose methods often put him at odds with the Winchester brothers. Gordon focuses on eliminating the supernatural simply because it isn't human, where the Winchesters—particularly as the series develops—are more willing to tolerate supernatural entities that are not actively killing humans. Gordon takes pleasure in considering himself a killer who freely resorts to torture, where Sam and Dean regard themselves as Hunters who only kill when they must and do nothing to their enemies that the situation doesn't force upon them.
When Gordon was 18 years old, a vampire broke into his house and abducted his sister. Gordon ran away from home, learned how to fight, hunt, and kill vampires, and tracked down the vampire who had taken his sister. He killed the vampire, and his sister, who had been turned, marking the beginning of his hatred for the undead. At some point during his career as a hunter, Gordon met John Winchester and Ellen Harvelle. Ellen described him as a skilled hunter in the sense that Hannibal Lecter is a good psychiatrist, being good at his job but dangerous to everyone else around him.
Gordon is introduced in the episode "Bloodlust", meeting up with Sam and Dean while hunting a nest of vampires. At first, Dean bonds with Gordon, but Gordon proves himself to be bloodthirsty and sadistic as he tortures one of the captured vampires, even though he knows these particular vampires feed off cattle blood and do not kill humans. After Gordon tries to force one of the vampires to drink Sam's blood while torturing her with dead man's blood, Dean, seeing the vampire resist the urge, ends up beating Gordon in a fight and leaves Gordon tied to a chair while the vampires escape. Later, while performing an exorcism, Gordon learns about the coming demonic war, Azazel's special children, and Sam's powers. In "Hunted", he kills Scott Carey- another of the 'special children'- and then tracks Sam down and tries to kill him, convinced that Sam and those like him are 'traitors' to humanity. However, Dean intervenes, and, after a scuffle, Gordon knocks Dean out, ties him up, and uses him as bait to catch Sam in a booby trap of grenades set with trip wires. Sam manages to evade the trap and knocks Gordon out. As the brothers leave the damaged house, Gordon regains consciousness and chases them, firing two pistols in their direction. The police arrive to subdue Gordon, based on an anonymous tip from Sam, and find his cache of weapons in his car.
In "Bad Day at Black Rock," Gordon is shown to be in prison, where he convinces a visiting fellow hunter to go after Sam Winchester, convinced that Sam was involved in the opening of the Devil's Trap regardless of Bobby's claims that Sam was actually trying to stop it. Gordon eventually escapes from prison and, once again, pursues the Winchester brothers in "Fresh Blood". However, he is captured and subsequently turned by a vampire. Gordon, however, turns on his sire, kills two other vampires, and then sets up a trap for the Winchester brothers, still convinced it is his duty as a hunter to rid the world of Sam Winchester. A fight ensues in a warehouse where Gordon holds a girl he has kidnapped—and turned—to use as bait, ending with Sam decapitating him with a garotte improvised out of razor wire.
According to series creator Eric Kripke, Gordon was originally going to learn about the hunter Sam killed while possessed and use it to convince more hunters to turn against Sam. This was intended to be a story arc stretching over multiple episodes. However, Sterling K. Brown was contracted for the Lifetime Television series Army Wives, and Lifetime would only allow him to return to Supernatural for two more episodes.