One inescapable fact about our species is that we're social animals: people are at the center of our universe. We have a long history of trying to understand the natural world by personifying its aspects. That's why believable characters make or break our stories.
A novel, however, is not a portrait. What readers really want is to see how interesting characters act and transform themselves over the course of your story.
This guide explores the structural underpinnings of character and characterization in terms of mythic cycles of transformation like the Hero's Journey and the Virgin's Promise. Once you understand these patterns your characters will ring true and your readers will believe in them, too.