The main character. A human social worker in New York City, employed by the Department of Integration.
- Anti-Hero: Type I.
- Badass Normal: He has his moments.
- Bastard Boyfriend: To his college girlfriend, Jacqueline. The psychological damage he inflicted to her not only lowered her self esteem, but drove her to throw her life away so she'd one day become perfect for him.
- Beleaguered Bureaucrat
- Chick Magnet: Subverted. Kind of. We don't see Mark get as many girls as Randall or even Leonard, but the girls he does get are flat out gorgeous (Lilith, Callie, Jacqueline) They also seem to form an obsession with him.
- Cultured Badass: His craftiness, quick wit and knowledge of how to behave in social situations gets him out of a lot of ugly situations.
- Designated Victim
- Dogged Nice Guy
- Geeky Turn On
Callie: Uno is like third base to him!
- Good Is Not Dumb: Some episodes show that he's a lot more on the ball than people think. Particularly the one where he's forced into selling his super-sized soul to Aldremach and gets it back by short-selling futures in the soul market, then spending the rest of the day debauching himself until his soul is the size of a pea. When Aldremach throws it out in disgust, he's able to get it back, along with 10 grand.
- Loser Protagonist: Mark is sometimes portrayed as this, in-show.
- Pungeon Master: Apparently, a recreational pastime of his.
- Sensitive Guy and Manly Man: He is the sensitive foil to both Leonard and Randall.
- Straight Man and Wise Guy: The straight man to Randall's wise guy.
- Trademark Favorite Food: Eggs. His obsession with them borders on the creepy.
- Understanding Boyfriend: Most of the time with his girlfriends, the only exception being his girlfriend in college, who he coldly dumped while she was in the hospital because she was allergic to eggs. Eggs he forced her to eat.
- Unfazed Everyman
- Unlucky Everydude
- Weirdness Magnet
- Zombie Advocate: His defining characteristic.
Mark's direct superior and on-again off-again girlfriend. A half-human succubus.
- Anti-Hero: Type V.
- Anything That Moves: Subverted. "Just because I've gotta have it doesn't mean I don't have standards."
- Attractive Bent Gender: As Dick. Complete with rippling muscles, Gag Penis, and the voice of H. Jon Benjamin.
- Bastard Girlfriend - She's pretty horrible to Mark most of the time, being half demon and hall. But the times she does open up to him and show him her human side, it's almost always a Crowning Moment of Heartwarming.
- BDSM: Callie's a big fan of this.
- Character Development: Has become somewhat nicer as the series progresses.
- Clothing Damage: Happens a lot, naturally, like when she transforms, or when she lactates fire.
- Comically Missing the Point: Very often, but mostly out of self-centeredness rather than stupidity.
- Destructo-Nookie: Callie is very active in bed.
- Green-Eyed Monster: Despite asserting that she's in an open relationship with Mark, she gets incredibly distraught when Mark actually does find someone else to have sex with.
- Half-Human Hybrid: Has a human mother and a demon father.
- Horny Devils: In "Soulsucker" it's shown that she even has the ability to suck souls out through the urethra.
- Power Is Sexy
- Really Gets Around
- Too Kinky to Torture
- Villain Protagonist
- Voluntary Shapeshifting: She has a larger, "more demonic" form with wings and talons. She can apparently extend and retract the wings at will.
Mark's slovenly zombie roommate.
- Anything That Moves: Including Great Brain's fiancée, and a blob creature.
Mark: It is literally anything that moves with you, isn't it?
- Bi the Way
- Brain Food
- Bromantic Foil: To Mark
- Catch Phrase: Whenever something bad happens, Randall lets out a drawn-out "craaaaaaap!!"
- The Slacker
- Straight Man and Wise Guy: The wise guy to Mark's straight man.
The wizard of social services, and Mark's co-worker at the DOI.
- The Alcoholic
- Ambiguously Human
- Berserk Button: "Shark Week is a national treasure!"
- Brilliant but Lazy: Often too lazy/drunk to do anything useful, but is actually quite knowledgeable and can accomplish a lot when properly motivated.
- Catch Phrase: "Magic!"
- Dismotivation: Leonard is a fairly powerful wizard, knows a lot about the bizarre processes of New York, and can be downright helpful at times. He's just very, very lazy.
- Mr. Exposition: Leonard is usually the one to explain the various fantasy elements in the series.
- Mundane Utility: His use of magic can fall under this sometimes, such as using his wand as a slideshow projector.
- Sibling Rivalry: He's jealous of his much more successful brother.
- Witch Species
- Wizards Live Longer: Somewhere in his fourth century.
A demon; Mark, Callie, and Leonard's superior at the DOI.
- Adult Child: When he goes to his family's house for Samhain, he wears goofy pajamas and reads comic books with a flashlight at night.
- He's also ecstatic over the prospect of going to Summer Camp, to the point of forgetting the reason for being there in favor of carving a (rather ornate) totem pole.
- He also can't poop away from home due to abandonment issues.
- Anti-Hero: Type V.
- Black and Nerdy: Twayne fits this to a T, given his voice and some of the stuff that happens to him (e.g. getting a nosebleed while traveling down to Hell due to the change in altitude). One of the few characters to pull this and Scary Black Man off simultaneously.
- Camp Straight
- Cannot Tell a Joke:
Twayne: What's the difference between a demonic council and a room full of chickens with their heads cut off? The chickens have far superior mid- to upper-level management skills! HI-YO!
- Casanova Wannabe
- Crouching Moron, Hidden Badass: As shown in "G.I. Wayne", if given proper motivation, Wayne has the capacity to take over the world with the forces of Hell.
- Gentle Giant: Though visually very imposing, Twayne is a big creampuff at heart, and highly naive to boot.
- Momma's Boy
- Pointy-Haired Boss: And he's got TWO POINTS.
- Scary Black Man: Ordinarily, demons on the show are portrayed as upper-class, WASPy types; Twayne is the only exception to date.
- Villain Protagonist
The chief of law enforcement, and a foul-tempered foil to Mark. Prejudiced toward non-humans, he'd rather see them all deported.
- A Father to His Men: Frank Grimes tries to be this, but given the High Turnover Rate of said men, they're understandably skeptical.
- The Atoner: He never quite got over having accidentally killed his partner in his rookie days. Turns out he didn't really... and later in life he accidentally shot him again.
- Character Development: In less than a season, he went from being an angry, frothing-at-the-mouth racist, violent cop to a mildly short-tempered clown who seems to berate the non-humans because he feels he's expected to.
- Gag Penis: Grimes' wang is big enough to be used as a bludgeon.
- Noble Bigot with a Badge
- Why Do You Keep Changing Jobs?: After he's fired from the DOI.
The highest ranking demon in Hell and Callie's father.
- Affably Evil
- Big Bad
- Corrupt Corporate Executive: Owns "Maggotbone Soul Industries", and is willing to steal Mark's soul for profit.
- Large and In Charge
- Names to Run Away From Really Fast: Seems to be standard for demons.
- Obnoxious In-Laws: Strongly dislikes Mark.
- Satan: Kind of. While he is referred to as "the Devil", this appears to be a title for the current head of Satan's line.