Antagonists create tension by challenging the hero's goals. The antagonist often has contrasting values or goals compared to the protagonist.
Pro Tip 2/3
Not Always Evil
Antagonists are not always villains; they might just have conflicting interests. In some stories, the antagonist might actually have sympathetic qualities.
Pro Tip 3/3
Cultural Awareness
Antagonists reflect cultural beliefs about right and wrong, which can vary. An antagonist's motives can be understood differently across cultures.