Professor Burris is the main character. He is also the narrator and commentator. This story is a sort of coming-of-age experience, although it occurs later in Burris's life. He undergoes the greatest transformation as a character. After his experience at Walden Two, he realizes it is more enlightened and functional than the current American society in which he has been living.
Frazier is the typical genius with some delusions of grandeur. His work at Walden Two impresses his visitors, particularly Steve, Mary, and Burris. His outlook on ethics, however, irritates Professor Castle. Frazier is the promoter of behavior modification in order to create a harmonious community. He views his ability to modify people's behavior as a godlike ability, as if he is creating a new sort of human.
Castle acts as the devil's advocate, constantly looking for philosophical, logical, and political failings at Walden Two. His character changes only somewhat over the course of the book. He is at odds with Frazier in most of the story, and he cannot accept the level of behavior modification in the community because he views it as robbing individuals of their free will.