Callie Maggotbone is Mark's immediate superior, and also his on-again/off-again girlfriend. In between stealing Mark away for bathroom rendezvous, Callie is berating him for being so soft. She's the typical 20-something girl who doesn't know what she wants, but is also bona fide hellspawn, as her father is a high-ranking minion of the Devil. However, since Callie is the product of that demon's union with her waifish human mother (who was drugged by a cult), Callie is frequently conflicted by her human side. She is drawn to Mark the nice guy, but feels in her heart that she will inevitably end up with someone like Twayne the Bone Raper...after all, it's what daddy wants. Unfortunately for all of us, such a union could potentially lead to the apocalypse.
Francis Grimes runs the Department of Integration's Law Enforcement Division, and like Twayne, has utter disdain for the immigrants. Preferring to think of them all as "illegal", he hunts down those who have strayed from the proper bureaucratic procedures that provide a path to U.S. Citizenship -- at which point Mark must step in to help. Grimes' encounters with unruly creatures have left him with a lifetime's worth of scars, both visible (missing kneecap) and emotional (broken marriage). Thus, he naturally detests Mark and anyone else who sympathizes with the immigrants. Grimes commands a small but well-funded goon squad that operates out of the D.O.I.'s "force floor."
Leonard Powers is a centuries-old wizard whose path has somehow led him to a desk job at New York's Department of Integration. This suits Leonard just fine, as his primary goals in life are to drink heavily and not rock the boat. In fact, he hasn't done any real work in years, relying on Mark (and his union, The Wizard's Guild) to save his ass. Leonard's brother is the famous magician Christ Angel, a fact that has bred a lot of resentment in Leonard, and probably contributed to his ongoing drinking problem.
Manhattan-newcomer Mark Lilly is a social worker at New York's Department of Integration. Having recently moved into his first apartment, a 2-bedroom he found on Craigslist, Mark discovers his roommate is freshly undead. Despite the frustrations of his job, where his boss Twayne has downsized Social Services to two people, Mark maintains a positive attitude. He has an on-and-off relationship with his immediate superior, an insanely hot (and completely insane) demon named Callie Maggotbone.
Randall Skeffington, Mark's roommate, "went zombie" in an attempt to win over a cute girl with a short-lived zombie fixation. Now, the unemployed/undead oaf spends his days doing odd jobs to pay the rent. Randall hails from South Jersey, a rabidly anti-zombie community, so he has been forced to hide his condition from his parents (especially his father, who fought in the Human-Zombie Civil War). Due to his zombie-ism, Randall is frequently losing body parts to decay, forcing him to find replacements at local flea markets.
Twayne the Bone Raper is a mid-level government bureaucrat who oversees New York's Department of Integration. He is also a terrifying demon, who would prefer tearing your spine out to giving you the time of day. Twayne loathes the immigrants and would rather vaporize them than help them, but he has to play ball, because infiltrating the U.S. government appears to be part of some larger demonic plan. Nonetheless, he despises Social Services and their compassionate ways, so he has slashed the department down to two people and allocated all of their funds to law enforcement. Despite his imposing appearance, Twayne is a bit of a high-status buffoon, often relying on Callie to make sure the department runs properly.