Antagonist - the character who strives against another main character. This character opposes the hero or protagonist in drama. The term is also used to describe one who contends with or opposes another in a fight, conflict, or battle of wills. In literature, this is the principal opponent or foil of the main character and is considered the villain unless the protagonist is a villain; in that case, the antagonist is the hero.
The word is derived from the Greek antagonistes, which means “rival” and was formed from the combining of anti, meaning “against,” and agon, meaning a “contest.”
Shakespeare’s plays provide apt examples of antagonists: his Macduff in Macbeth is an antagonist and the hero, since the protagonist—Macbeth—is a villain; Laertes and Claudius are the antagonists of Hamlet in the play of the same name; Iago is Othello’s antagonist in Othello. Also, the antagonist does not have to be another person. In Jack London’s story “To Build a Fire,” the antagonist is the bitterly cold weather.