Callie is a female half-demon, or more specifically, a succubus. Her father is Aldermach Maggotbone, who is also known as the Devil. Her mother is a mortal human called Rosie, so Callie is also half-human. She is Mark Lilly's boss and girlfriend. Her mother gives birth to her sister Lillith in season 2.
She was born in October 27th, 1981 and is 5' 7" tall, as revealed in the episode "Better Off Undead".
Callie starts a relationship with Mark at the start of the series where they sleep together for the first time. One of the reasons she is attracted to Mark is his constant fear that she will kill him.
Yet Callie believes that she is destined to unite with Twayne which would somehow lead to the End of Days, as very visually seen in her dream in "Kong of Queens". This is the only reason she would ever consider a union with Twayne as she is disgusted by practically everything else about him. Deep inside, however, she knows that one day they will end up together since that is what her father wishes for her.
Callie kills all of her old boyfriends to purify herself for Mark after he has gifted her a puzzle box in her Zechalech ceremony in "Soul Sucker". When he later finds out she is to suck out his soul in the end, he reneges on the whole deal, yet Callie does not press him.
Callie finally gets off the hook from her marriage to Twayne when her mother Rosie gives birth to her little sister Lillith. Aldermach arranges Lillith to replace her for the marriage. In the end Lillith intends to kill Callie but gets killed instead.
She has been changed by Mark and turns good in "The Ring of Powers". Aldermach gets tremendously abhorred and orders a hit on her. When her life hangs dangerously by a thread, her savior turns out to be Doug.
At the end of season 2, she has been "engaged to be engaged" to Mark.
Callie's mood tends to change very often and drastically, resulting in her breaking up and getting back together again with Mark very frequently. Mark once referred to this as being "more schizoid than normal."
She is extremely sadistic, occasionally hurting Mark and getting turned on by violence given to others.
Also she is very sociopathic, as in "Attack of Mark's Clone", she is perfectly willing to injure, kidnap, and confine Mark just to win a bowling game. On one occasion she referred to Mark as her "human sex slave", however in other episodes she seems to actually care for Mark.
- Callie's "three-hole" opens up in the episode "Demon Baby".
- She speaks the manbird language, as revealed in "The ManBirds".
- Due to her demon side, she has a very high body temperature. Once she complains about not feeling well, Mark feels her forehead, winces in pain as his hand gets burnt and replies, "No hotter than usual." ("Ride Me to Hell")
- She has a garden of petunias.