In a recent email, Roy Williams, the Wizard of Ads, made this statement:
Tell me what a person admires and I’ll tell you everything about them that matters.
He tied this to the idea of image, the picture of ourselves we try to create for the world--which probably isn't paying attention, by the way.
It's a good way to think about a character as well as about real people. If you know what your character admires, and the image he or she wants to project, you know a lot. And if you know how that image differs from who they really are, you know even more.