Once you know who your hero is, you automatically know who your villain is. That’s because your villain is the anti-hero but stronger and more powerful. In “Rocky,” the hero is boxer but the villain is the heavyweight champion of the world. In “Avatar,” the hero is a Marine but the villain is the Marine commander. In “Die Hard,” the hero is a cop, but the villain is an equally skilled and intelligent thief. Your villain is always the opposite of the hero.
As your story progresses, what creates suspense is that your hero must be constantly tempted to become the villain. This is most apparent in “Return of the Jedi” where the hero (Luke) is tempted by the villain to join the dark side and become like his father (Darth Vader). In “Coco”, the hero wants to become a musician and is willing to abandon his family to pursue his dreams. Yet that’s exactly what the villain did, abandoning everyone for his own selfish glory and that’s the path the hero risks following as well.
Make the hero risk temptation and becoming the villain. In “Terminator 2,” both the hero and the villain are Terminators. The difference is that the hero is using his power to protect and preserve lives while the villain is using his power to destroy and take lives. The hero could be tempted to take lives to achieve his goals, but he refuses despite the temptation that doing so could be the easiest path to solving his problems.
If your hero doesn’t risk becoming the villain, then your story won’t feel as suspenseful. The hero and villain must be balanced against each other where the hero risks becoming the villain if he or she fails to change. Lead your hero into temptation because when the hero realizes how close he or she has come to becoming like the villain, that can be an emotionally charged moment. Think of Luke staring at his robotic arm in “Return of the Jedi” and realizing he’s becoming part machine just like Darth Vader.
Bring your hero on the verge of becoming the villain. Then make the hero realize how horrifyingly close he or she has come to changing for the worse. That will make your hero more sympathetic and noble when he or she refuses to become like the villain and instead chooses to become a better person.