All stories need an antagonist, but the antagonist doesn’t necessarily need to be a person. It could be the environment the hero finds themselves in, their own inner demons, society itself. A villain is a type of antagonist: the “bad guy” who opposes the hero of the story and causes problems.What makes a great villain? – The History Quill
From a reader’s perspective, what makes a villain compelling is their depth. They need to be someone with backstory and motivations that go beyond simply stopping the hero. This all influences the sort of troublemaker they are and the journey they go on. Are they the embodiment of evil? Are they a friend who betrays the hero? Are they the exact opposite of the hero, or very alike? Will they be redeemed, or stay a villain?