Each character in any work of prose should adhere to at least one of these:
1. They represent a concept, heavily rooted in theme
2. They support a concept, heavily rooted in theme
3. They represent a person, place, or group known to the author, rooted in the "real world"
4. They help further the plot, expand upon setting, and/or develop other characters
5. They are interesting enough to carry the story on their shoulders
6. They create/deepen conflict
7. Comic relief
Did I miss anything?