Willow

 is a ghoul, the self-proclaimed gatekeeper of the Underworld. She can usually be found on the Mall, wandering around just outside the entrance to the Museum of History.

Trivia
The character is possibly a reference to Alyson Hannigan's character "Willow Rosenberg" in the TV series Buffy the Vampire Slayer.

Appearances
 only appears in Fallout 3.