Your hero can’t change all by himself. To change, your hero always needs the help of a Mentor. However, the Mentor character doesn’t just pop up solely to help the hero. Instead, the Mentor needs a back story of his own. Basically, your Mentor needs to be pursuing a goal too.
In Act I, your Mentor has an unresolved problem from the past.
In Act IIa, your Mentor teaches the hero a lesson that represents your story’s theme.
In Act IIb, your Mentor helps your hero somehow.
In Act III, your Mentor resolves his problem from the past through the villain.
In the remake of “The Karate Kid,” the Mentor is the karate teacher. In Act I, this karate instructor feels bad for what happened to him in the past. In Act IIa, this karate instructor teaches the hero how to fight. In Act IIb, this karate instructor helps the hero when he hurts his leg. In Act III, this karate instructor inspires other students to come to him to learn karate.
In “Star Wars,” the Mentor is Obi-wan. In Act I, Obi-wan feels bad for creating Darth Vader. In Act IIa, Obi-wan teaches Luke about the Force. In Act IIb, Obi-wan turns off the tractor beam so Luke can escape from the Death Star. In Act III, Obi-wan faces Darth Vader and resolves his past.
In “Harold and Maude,” the Mentor is Maude. In Act I, Maude tells Harold about her upcoming birthday and how it’s a perfect time to end it. In Act IIa, Maude teaches Harold how to look at life as a gift. In Act IIb, Maude schemes with Harold to trick his uncle so he won’t put Harold in the army. In Act III, Maude resolves to die so she can leave life at the right time.
Your story’s Mentor needs a past and a goal to achieve through the actions of the villain. When your Mentor has a strong goal, then your story feels much stronger, especially when your Mentor’s goal reflects the story theme like your hero’s own goal does. Then your Mentor’s goal reinforces the theme and highlights the hero’s actions as well.
Make sure your Mentor has a strong goal and you’ll go a long way towards creating a much stronger story.