Black Aliss, or Alison Weatherwax, was an incredibly powerful witch in Terry Pratchett's Discworld. She knew all the tricks a witch should know, and had mastered stories... A major subset of the Discworld novels of Terry Pratchett involve the witches of Lancre. They are closely based on witches in British folklore, combined with modern Wicca and a slightly tongue-in-cheek reinterpretation of the Triple Goddess. Witch magic is very different from the wizard magic taught in... Nanny Ogg said she could be running as many as three of them at once. Unfortunately, after a while she was unable to distinguish reality from her stories and started going mad- hence the name Black Aliss. She's the wicked witch mentioned in popular fairy tales, and met her end when she was pushed into an oven (a la Hansel and Gretel).

Aliss was a A major subset of the Discworld novels of Terry Pratchett involve the witches of Lancre. They are closely based on witches in British folklore, combined with modern Wicca and a slightly tongue-in-cheek reinterpretation of the Triple Goddess. Witch magic is very different from the wizard magic taught in... Granny Weatherwax's own grandmother, as revealed by Count De Magpyr in Carpe Jugulum...he mentioned a Weatherwax had come through Uberwald some 50 years before to combat vampires. This led Granny to believe that Aliss had not turned comepltely evil, even at the end. Granny is equally powerful as Aliss was, if not moreso, and is concerned constantly with keeping herself in check lest she end up like Aliss.