From the introduction:
There are scores of sourcebooks providing classes, templates, and models for characters based on the categories of powers and abilities they possess. But what about personalities? This booklet provides archetypes for three common sets of character motivations, values, and interactions. They are broad and adaptable, and intended to help guide you in determining how your own character might behave. Each archetype is intended to provide you with ideas on how to better roleplay your character.
Within this supplement you'll find a Protagonist archetype, the Leader, meant for player characters; an Antagonist archetype, the Mastermind, designed for villains; and a Supporting Character archetype, the Mentor, for use with other types of non-player characters.