on Writing Forward:

The hero, the mentor, the sidekick. We’re all familiar with archetypal characters in storytelling. We’ve seen them before. We know the roles they play.
Archetypal characters shouldn’t be confused with stock characters or stereotypical characters. Although we’ve seen all these characters before and will surely see them again, stock and stereotypical characters are based on character traits; archetypes are based on the characters’ purpose within a story.