“I love this life because it’s all black and white. There’s no maybe. You find the bad thing, you kill it. Most people spend their lives in shades of gray, but not us.”

—Gordon Walker, “Bloodlust” (2-3)

Let’s say that you have a demon hunter who is dedicated, smart, resourceful, focused, and who makes the world safer for ordinary folks day in and day out. Let’s say that this guy will do whatever it takes to rid the world of demons, monsters, and other nasties. Let’s say this guy falls at the hands of a traditionally awful sort of creature, a vampire, but although he becomes one himself, he somehow keeps a remnant of himself and tries to carry out one last mission to save the world. Sounds like a great guy, right? Maybe even a hero?

Not if he’s Gordon Walker. For a character who only appeared in a whopping four episodes (“Bloodlust,” “Hunted” [2-10], “Bad Day at Black Rock” [3-3], and “Fresh Blood” [3-7]), this character developed into one of the most complex that we’ve seen on the show: a bad guy who honestly believed that his efforts led toward a better, safer world.

Why have a villain who isn’t, well, supernatural? Because a character like Gordon is essential, both for establishing who hunters are as a group and for taking a closer look at the Winchesters themselves.

For the structure and mythology of demon hunters to be fully established, the series needed to show what rules hunters  …