Check out Enotes.com's awesome Guide to Literary Terms and get a deeper insight on this interesting topic. According to our guide, the literal definition of an antagonist goes as follows:
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.
Now, let us work backwards and say a NON example of what is an antagonist. The opposite of the antagonist in literature is the protagonist, as you may know.
The protagonist is the central figure of a story or novel. It is the protagonist's point of view that serves as the narrative of a story. It is also the person that is at the center of the problem of the story.
The situations that affect the protagonist are the focal point of the narration. Now, the protagonist may or may not tell the story from his or her own POV. When it happens, it is known as "first person" point of view. Otherwise, literature is narrated through another set of eyes in third person.
The antagonist, then, is the opposite force in a drama. It is the contrasting figure that directly opposes the actions and thoughts of the protagonist, hence, it "antagonizes" or challenges him or her.
This being said, do not assume that only an individual can be an antagonist. There are other variables that can definitely serve as antagonists, causing the protagonist to be in conflict. These variables include:
- protagonist versus self (personal demons and limitations are the antagonists)
- protagonist versus the world (society, the environment, the weather, established rules, ethics, politics, and regulations are the antagonists)
- protagonist versus destiny (disease, death, crime, poverty, disaster, and other inevitable and tragic events can be antagonists)
- protagonist versus divinity (any system of belief, deity, God himself, Karma, or any other thing considered spiritual are the antagonists)
Therefore in literature, as in life, anything that comes in between a protagonist's ultimate success, or completion of a milestone, is considered an antagonist.