antagonist
n.the main character who opposes the hero in a story, film, or play. You use this word to describe the person creating conflict for the main character.
n.the character or force that opposes the protagonist in a narrative work. In literature and drama, it represents the primary source of conflict.
“The antagonist tries to stop the hero from winning.”
“In the novel, the antagonist is a corrupt politician who blocks the hero's plans.”
“The antagonist's complex motivations transformed him from a simple villain into a tragic figure driven by personal loss.”
“With its oil-export routes once again under threat, Saudi Arabia is stepping up its military campaign against an old antagonist.”
From Latin antagonista, from Ancient Greek ἀνταγωνιστής (antagōnistḗs, “opponent”) (ἀντί (antí, “against”) + ἀγωνιστής (agōnistḗs, “a combatant, pleader, actor”)), from ἀνταγωνίζομαι (antagōnízomai, “to antagonize”).
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.