The antagonist is an "anti""agonist" which is against binding, or against a kind of organic fruition. The antagonist is certain as death and taxes and when used in direct opposition to the protagonist assures that a text resembles a tennis match: yes, only one of you can win. There will be dropped balls, someone might throw a tantrum, but everyone will wear white, use tennis rackets, and yes, we are headed down a very narrow, confined chute toward "outcome."
Antagonists are often exaggerated and can be entire cultures, or moments, or multiple entities all against the protagonist. Consider poor Tess of the D'urbervilles who, facing serial publication, was thrown hurdle after hurdle for the sake of a weekly payment as she hurtled toward certain death.
An antagonist can also be language, or in language.
see also "anti-hero" "Language Poetry"