Story structure
Villain
A cruel, malicious character devoted to wickedness or crime; structurally the opposite of the hero and often the plot's evil agency.
A villain is a fictional character "defined as a cruel and malicious person," devoted to wickedness or crime, or serving as "an important evil agency in a plot." The word descends from Old French vilain, of Late Latin villanus origin, a farmworker, later a person below knightly rank, and the perceived "lack of chivalry and courtesy" fed the modern sense. Structurally, "the villain's structural purpose is to serve as the opposite to the hero character"; Roger Ebert put the craft stake plainly: "Each film is only as good as its villain." Iago, Richard III, Darth Vader and Lord Voldemort anchor the roll call.
The term is the moral extreme of the antagonist: an antagonist merely opposes, a villain is evil, and an antihero "fights on the side of good" with questionable motives. The making of one, voice, reason, scale of cruelty, is how to write a villain; this entry is the definition that guide builds on.