Central protagonist Dr. Susan Calvin is the developer of robopsychology and part of the team at US Robotics that fashions robots into a major force for good. Dr. Calvin feels a great sympathy for humanoid machines, whom she believes make better people than do people themselves. She is solemn and distant—she also broods over her belief that she’s not attractive to men—but brilliant and passionate about her work.

Dr. Calvin is introduced at the outset as part of the book’s frame story that shapes the chapters into events in her life. Her vigorous support of robotics as a public good makes her the moral center of the novel; her journey is from fascinated student of robot psychology to staunch supporter of robots as citizens.

A polished and gentlemanly attorney, Stephen Byerley campaigns for mayor of a US city but runs into accusations that he is a robot, a being forbidden to reside on Earth. He never seems to eat or sleep, and he always obeys the Three Laws of Robotics. Byerley settles the issue by punching a bystander, which violates the First Law against causing harm to humans and vindicates him.