Death Eaters are fictional characters in the Harry Potter series of books by J.K. Rowling. They are characterized as evil wizards and witches who have allied themselves with Lord Voldemort in his efforts to take over the world, kill all witches and wizards born to non-magical parents for being "mudbloods" and enslave all non-magical beings as well as seeking to opress non-human magical creatures such as goblins and elves. They believe that people of pure magical ancestry known as Pure-Bloods are superior to those of only partial magical ancestry, whom they call Half-Bloods. Nonetheless not all Death Eaters are Pure-Blood. Their leader Lord Voldemort originally known as Tom Riddle is Half-Blood because his father was not a wizard. The Death Eater spy turned double agent Severus Snape is Half-Blood because even though his mother was a witch his father was not a wizard. Fenrir Greyback is allowed to be a Death Eater even though he is a werewolf. Hermione Granger observes that a lot of Death Eaters must be Half-Blood because there are too many for them all to be Pure-Blood.