Rachel (The Simpsons)

Rachel is a villain from The Simpsons and a parody of horror villains, common to the Simpsons "Treehouse of Horrors" style stories, which while non-canon to the show itself are popular among fans and exist in their own separate portion of the Simpsons mythos.

Rachel is the imaginary friend of Lisa Simpson who somehow gained life and became a malevolent thought-form intent on killing all of Lisa's friends so as to keep Lisa as her "best friend" forever, she also sought to kill Marge for being the one that helped Lisa move on from her imaginary friend in the first place.

Ultimately Rachel is defeated when Lisa uses her own imagination to age Rachel into her own "mother", causing Rachel to fade away.