A werewolf is a mythical lycanthropic monster, having both human and lupine (wolf-like) characteristics. Werewolf mythology originated in the folklore of Europe, but has been popularised around the world in various fantasy and horror fiction and films.
Werewolves assume human form for much of the time, but transform into wolves, traditionally when the full moon rises. In some werewolf fiction, a werewolf's bite can cause a person to develop into a werewolf. This aspect of the myth probably derives from similar myths about vampires.