Generate a Compelling Antagonist Who Is Not Simply Evil

Antagonists who are simply evil are simple to write and simple to dismiss. The ones that make a story worth reading believe they are right, have a motivation a reasonable person could understand, and hold up a mirror to something the protagonist cannot avoid. This designs that antagonist: their world view, what drives them, how they reflect the protagonist, and the moment readers will find themselves uncomfortably on the wrong side.

I am writing {STORY_TYPE} and I need an antagonist. The conflict is with the protagonist {PROTAGONIST_DESCRIPTION}. Help me design an antagonist who has a coherent internal logic: they believe they are right, they have a genuine motivation that a reasonable person could understand even if not agree with, and they represent something the protagonist must confront about themselves or the world. Give me: the antagonist's world view in one sentence, the specific grievance or goal that drives them, the way in which they are a dark mirror of the protagonist, and the moment when the reader will find themselves uncomfortably sympathetic.