"I have a scar, which I didn’t have before," declares Jared Harris, the you'd-know-him-if-you-saw-him British actor best known for his roles on "Mad Men" and Fox's now-defunct "Fringe." "A good prosthetic scar, a wig, a white wig. Kind of a grey hair wig, stuff like that. Which is a bit shocking. You look in the mirror and you see what you might be like a couple years from now."

Of course, this rather involved hair-and-makeup process just comes with the territory of playing Hodge Starkweather, a duplicitous Shadowhunter in the books who in a past event referred to as the "Uprising" teamed with Meyers' Valentine in an attempt to kill off every demon and "Downworlder" in existence. As punishment for his transgressions, which resulted in a war that caused many Shadowhunters and Downworlders to lose their lives, Starkweather was cursed to remain within the walls of the New York Institute for all time, and what's more to serve as a teacher to young Shadowhunters coming up through the ranks. Call it a lifetime sentence of community service, "Mortal Instruments" style.

"You don’t know which side he’s playing on, which is always interesting to do," Harris says of the character, who in the actor's words "drip-feed[s]" information to Clary throughout the film without ever revealing the whole truth. "He does a couple of 180s in the story."

Not surprisingly given his demographic, Harris was unfamiliar with Clare's book series prior to signing on but was drawn to the film by what he saw as the "moral conundrum" faced by Starkweather.

"That’s what was interesting about the character, is someone who knows what the right thing to do is, but for his own reasons, is making a different deal, because he’s trying to change his circumstances," says Harris, his neck "tattooed" with a large rune. "But he knows the difference between the right thing and the wrong thing to do, and he’s not delusional in the sense that he [thinks] that he’s doing something for the betterment of mankind or some bullshit like that. He knows that what he’s doing is purely to get his own ass out of the situation that he’s stuck in."

But who gives a rip about thematics? This is "The Mortal Instruments," for crying out loud. What we really care about is seeing Harris go mano-a-mano with, say, his 7'1" "Sherlock Holmes" co-star Robert Maillet. "What’s great fun is I get to fight Dredger from 'Sherlock Holmes,'" says Harris of the WWF star-turned-actor, who plays the role of Valentine henchman Samuel Blackwell. "He’s a fucking enormous man. So it’s been fun, because really, when you do all these fight scenes, you try and jazz ‘em up and everything. And then I sit there and I go, 'Listen, if this guy hit me, I’d collapse. I’d crumble if he actually managed to connect with me.'"

Harris' extensive filmography is certainly made up of a wide variety of genres, but 2012 proved to be the year of the occult for the actor, who in addition to his role in "The Mortal Instruments" filmed the final season of "Fringe" (reprising his role as the power-mad David Robert Jones) as well as an upcoming supernatural horror movie entitled the "The Quiet Ones."

"This year, I’ve done three, for fuck’s sake!" he says of his recent string of horror-and-fantasy-themed projects. "What’s going on? I’ve done three. I did a movie called 'The Quiet Ones,' which was about a guy who’s investigating paranormal events...but of course, because it’s a horror movie, it all goes terribly wrong. And then I played the Devil. And then now I’m in this film, which is all about demons and shit, so yeah. It’s been a weird year for that."

A former contributor to sites including MTV's The Backlot and Bloody-Disgusting, Chris Eggertsen worked in film development before indulging his love of pop culture writing full time. He specializes in horror, the intersection of social issues and entertainment and Howard Stern. He's on Twitter @HitFixChris.