It's weird because both words come from Greek except here no one calls the bad guy an "antagonist", and protagonist just means the main person. Antagonist means "competitor", but not specifically in terms of a movie or play or whatever, just generally "competitor". Not even "adversary" in general. I'm not sure who (when, why) decided it is specific to cinema and literature and that it means "bad guy" and protagonist means "good guy" but it really annoys me when I see it because it clashes against what I know the words being used for, and also it creates a game of broken phone because some other countries also don't use the words like that. Also "main characters" and "secondary characters" is a much less silly categorization than "good guys" and "bad guys".