Played by: Alyson Hannigan
Willow started off as a meek witch in high school, dabbling with spells and trying to help Buffy. But she met Tara and became quite the force to be reckoned with. And of course, the magic eventually was too much for her and she became addicted to it, finally going full-on evil in the wake of Tara's death. Thank God for that yellow crayon.