Born sometime in the 1760s, in a village near Norrköping, Sweden, Eli was originally a boy named Elias, but was castrated by a vampire as part of a ritual when he was 12 years old. He became a vampire himself, and over the years developed a more feminine personality.Though she used to be a human, she's not considered as a half-vampire because she can't control her thirst for blood. She can resist cold temperature. When throwing tantrums and went inside someone's house without being invited, blood flows from her eyes, ears and nose. In both versions of the film she is able to fly and verbally states that she can.
When we meet Eli, "she" has a caretake companion named Hakken, a pedophile she recruited to help her. Hakken believes he loves Eli and will do almost anything for her, including procure her food (i.e. fresh human blood). He proves less than competent at this.
Eli's name is changed to "Abby " in the American funded motion picture Let Me In (2010) andn a four-issue graphic novel associated with the film. She was portrayed by actress Chloe Grace Moretz.
Abby's last name remains unknown, although she says her age is "twelve, more or less" adding later "I've been twelve for a very long time." In a deleted scene we see her attacked and transformed. The actress claims she and the director worked out that Abby had been attacked by her uncle.The nature of Abby's vampirism is virtually identical to that of Eli in Let The Right One In. She can only consume fresh human blood and without it she grows weak, possibly even begining to decay. Her bite is instantly infectious which is why she tries to prevent her victims from fully transforming by breaking their necks. She is a shape-shifter (including evidently the power to grow functional wings), does not feel the cold, and exhibits extraordinary strength. Lke some folkloric undead, she has a fascination with puzzles. Unlike Eli, however, she seems to have begun to enter puberty when becoming a vampire. Her relationship with the twelve-year-old boy Owen has a distinct quality of flirtatiousness to it. It seems pretty obvious she was born female. She also has what might be called a "game face" like the vampires of Buffy the Vampire Slayer or The Lost Boys. In this form she has a very different voice and seems considerably more bestial. In the film and graphic novels, we see her with a caretaker/companion named Thomas, a man well into middle age who seems jealous of her attention. Evidence strongly suggests they've been together since he was approximately twelve years old. Their relationship has deteriorated into bitterness but there remains some real affection at times. Thomas procurs blood for Abby by murder. He would be considered a serial killer. In order to protect her, he keeps a container of acid with him while hunting. When he is caught, he pours it over his face to make identifying him impossible or at least more difficult. He survives this experience. Abby visits him in the hospital, where Thomas offers his blood to her. She takes it, killing him. His fall from the tenth floor afterwards presumably precludes his becoming a vampire.
Abby forms an emotional bond very much like love at this time with the boy Owen, a bullied child who lives in the apartment next door to hers. Ultimately, when he is nearly killed by four bullies in his school's swimming pool one night, she bursts in and slaughters them all. He is seen on a train with her at the story's end, tapping morse code to each other through the traveling chest in which she hides from the sun. The implication is that he has taken Thomas' place.
When exposed to direct sunlight, Abby burns. She also cannot enter a private residence without someone's permission. Public places like the lobby of a hospital or a school gym evidently don't count. Whether she needs a distinct invitation every time or just for each entry-way never becomes clear. If she enters without permission, she begins to shake and bleed out from her ears and skin. She herself does not understand this process.