Think of your theme and that defines your hero’s beginning and end. For example, the theme in “Terminator 2” is that “Killing is wrong.” Therefore the hero (the good Terminator) begins the story thinking killing is okay. By the end, the hero learns that killing is wrong when he finally understands why humans cry.
Once you know your theme, you automatically know the starting and ending point for your hero, which defines the hero’s change. Then you also know your villain because your hero could become the villain if he or she doesn’t change. In “Terminator 2,” the hero could become evil if he continues killing people.
Based on your villain, you also know your mentor because your mentor is someone with powers but with a haunted past. In “Terminator 2,” the mentor is John Connor and his haunted past is dealing with his frayed relationship with his mom. By the end of the story, the mentor (John Connor) has finally established a relationship with his mother once more because he realizes she was right all along and wasn’t a nut case.
So once you’ve denied your theme, you can define your hero.
Once you know your hero, you also know your villain.
Once you know your villain, you can define a mentor as someone similar to the villain but with a haunted past that he or she needs to overcome.
Your hero, mentor, and villain are all similar. They just all exhibit the theme in different ways. If you create a villain or mentor that’s wildly different from the hero, they won’t be a suitable match. Imagine the hero in “Thelma and Louise” trying to fight against the villain in “The Matrix.” It won’t make sense because the hero and villain are form different worlds. When the hero and villain are similar, that makes the hero more likely to become the villain if he or she doesn’t change. That makes the hero’s transition and change more crucial so he or she doesn’t become like the villain.
Your hero, mentor, and villain are more alike than different. Make sure your hero, mentor, and villain are similar.