El Diablo
From The Vault
The guy's name is Miguel Vargas, but he calls himself "El Diablo., and is from Denver. He went crazy one night and killed six people in two different homes. They call him the "Vampire Killer" because he bit his victims on the neck during or after killing them. Last anyone heard he went east. Bob the Bounty Hunter in Hoover Dam has a wanted: dead bounty on his head. When he dies he drops a severed head item. Bob knows a guy who was going to look for El Diablo here in Dogtown, but he never came back (because El Diablo killed him).
El Diablo is insane. He really thinks he's a vampire. He refuses to come out during the day (he's only findable at night) and says he started killing that night in Hoover Dam because "some bitch stole his hat," which is a Cat In The Hat-type hat.

