I'm a personality - like a George Plimpton who effectively plays himself in a bunch of different roles, or a Paul Lynde-type character.
Comics have a problem, and that is continuity - the obsession with placing the characters in an existing world, where every event is marked in canon. You're supposed to believe that these weepy star boys of now are the same gung-ho super teens fighting space monsters in the '60s, and they've only aged perhaps five years.
One of the things about crowd work that's so exciting is when you discover a character in the audience who's interesting or funny, who you can vibe off of. If someone's got a weird job that you can make reference to throughout, or you can bring that person onstage - humiliate them, or celebrate them! You can put people in conversation with one another. The best is when something that they're doing can reflect back on something that you're doing.
The villain of any story is often the most compelling character.
