Good villains are relatable. Their motivations are clear and believable. Often, a villain has the same core desire as the hero. The best villains are someone else’s hero.
In the same way, a good hero should be someone else’s villain. The hero stands for something, often in the face of a hurtful power structure. To that power structure’s defenders, our hero is a villain. Additionally, the tastiest heroes have fundamental flaws that may test the reader’s sympathy. Even better if their flaw is bound to their core desire. In this way, the hero and villain flesh each other out.
For a simplified example, Hamlet seeks justice for his family, while Claudius wants to maintain control. The tragedy grows out of Hamlet’s ruthlessness, a trait he shares with his uncle. In his rebellious way, Hamlet becomes an enemy of the court – their villain. Conversely, Claudius has sympathizers. Maybe somewhere there is a story about King Hamlet and how he had it coming.
That’s an OK start. Who is your favorite hero? What is their central flaw? How are they nearly the villain of their story? Do they improve on their flawed trait in a meaningful way?