Vengeance demons are a group of beings that appear in the TV series Buffy the Vampire Slayer. They are immortals who travel the world exacting vengeance on behalf of victims, such as scorned men, women or neglected children. Some of them, according to Halfrek in the episode "Older and Far Away", prefer to be called justice demons, which carries less stigma than 'vengeance'; the term "vengeance demon" itself was first used in "Pangs". Their typical method is to encourage a wronged person to vent spleen about those who have hurt them. The moment the object of the demon's attention expresses their preferred method of punishment in the form of a wish, the vengeance demon can cause his or her wish to come true, whether it requires gruesome dismemberment or even the creation of a new alternate universe (as in "The Wish").
Two vengeance demons have appeared in Buffy the Vampire Slayer: Anyanka (also known as Anya) and Halfrek (sometimes called Hallie). Anya, the more prominent of the two, specializes in punishing men who have scorned women. She loses her powers and became human, eventually falling in love with Xander Harris and becoming a member of the Scooby Gang. Halfrek's principal concern appears to be children abandoned by their families. She has appeared periodically, often to encourage Anya back into her demonic ways.
The vengeance demons are led by a male demon, D'Hoffryn. D'Hoffryn appears to human women who have used spells or witchcraft to exact notable revenge on their loved ones, and transforms them into demons if they agree to take the "job". In a flashback in "Selfless" D'Hoffryn recruits Anyanka, and in "Something Blue" he fails to recruit Willow Rosenberg.
Marti Noxon, who introduced vengeance demons to the Buffyverse in the season three episode "The Wish", has revealed that she was inspired by a discussion of goddesses in the Introduction to Feminisms course taught by Bettina Aptheker at the University of California, Santa Cruz.
Despite the severity of the vengeance they inflict, vengeance demons are comically portrayed as white-collar workers. Throwaway comments by Anya, Halfrek, D'Hoffryn all suggest an office-like setting, where demons relate their stories of vengeance and gossip to each other. At one point, Anya is required to file a flightplan before teleporting.
Overall, vengeance demons appear similar to the classic depictions of genies, as they obey the exact wording of a wish but do not give the wisher what they want. For example, Cordelia Chase's wish to Anyanka that Buffy Summers had never come to Sunnydale results in an alternate history where the Order of Aurelius, a centuries-old vampire cult, rules the town with an iron fist ("The Wish"), while Dawn Summers's wish to Halfrek that nobody would leave her causes the guests at Buffy's 21st birthday party, as well as anyone else who enters the Summers residence, to be trapped inside ("Older and Far Away").
- Vengeance Demons (Buffy Trivia Guide)