Possibly expanded on best through the use of superheroes and super-villains. If anyone is going to make a good fictional character, the first step they need in making one is to give them a detailed background and/or origin story. The best way to further expand a character is to give the readers/viewers a deeper look into their past lives (such as their childhoods for example) and to see the reasons why they developed into the people that they’ve become. It doesn’t matter whether or not they are good guys or bad guys, if any of them have more of a story behind their character, then they will be able to be more individual from the rest of the characters of the story, and therefore more likable in their own unique way. Even if they don’t have an explained origin behind their character, having one will help the readers/viewers connect with them more.