Dr. Susan Calvin is the world's first robopsychologist at US Robot and Mechanical Men Inc. She is a brilliant, serious, and somewhat distant scientist who often prefers the company and logic of robots over human beings. Throughout her long career, she investigates complex psychological dilemmas in malfunctioning positronic brains, working constantly to prove that robots are a benefit to humanity.

Stephen Byerley is a polished and highly effective attorney campaigning for political office. He campaigns on the rights of the individual citizen and refuses to submit to physical tests that would disprove rumors that he is secretly a robot. He maintains a flawless ethical record, raising complex questions about whether a perfectly law-abiding public servant might actually be a machine bound by the Three Laws of Robotics.

Gregory Powell is a senior robot technician for US Robots. He and his partner are frequently assigned to difficult, hazardous outposts on remote planets and space stations to evaluate experimental machinery. He is the more intellectual and commanding of the duo, relying heavily on his deep understanding of positronic brains to solve dangerous technical glitches.

Mike Donovan is a field technician for US Robots who travels across the solar system assembling and managing complex robotic equipment. Red-headed and quick-tempered, he provides a more emotional, action-oriented counterpart to his partner's logic. He frequently complains about their miserable assignments but proves highly capable when survival is on the line.

Francis Quinn is an ambitious politician running against Stephen Byerley. Suspicious of his opponent's flawless record and unusual personal habits, Quinn attempts to leverage the public's inherent fear of artificial intelligence to win the election. He represents the reactionary factions of humanity that resist the integration of robots into society.

Peter Bogert is a highly skilled mathematician and smooth-talking administrator at US Robots. Ambitious and confident, he often believes he knows better than his colleagues. He regularly clashes with Dr. Calvin over robot psychology and is eager to climb the corporate ladder, hoping to eventually replace the current plant director.

Dr. Alfred Lanning is the elderly, crusty director of US Robots. He possesses a deep understanding of the company's patented positronic brains. Though he frequently bickers with his subordinates, his leadership and decisive input are essential when the company faces potentially disastrous robotic malfunctions.

Gloria Watson is an eight-year-old girl who forms a deep, emotional attachment to Robbie, one of the earliest models of a non-vocal nursemaid robot. She views the machine not as a tool but as a beloved friend and playmate. When the robot is taken away due to societal prejudice, her persistent grief forces her parents to reconsider their stance.

Robbie is an early, non-vocal nursemaid robot manufactured in 1996. He is designed specifically to care for and entertain children. Despite his lack of speech, he exhibits immense patience and a gentle disposition, serving as a loyal companion to young Gloria despite the growing societal prejudice against his kind.

George Watson is Gloria's father. He is a pragmatic man who initially finds their robotic nursemaid highly efficient and safe. Though he caves to his wife's demands to remove the machine from their home, he attempts to orchestrate a trip to New York to help his daughter recover from the loss of her friend.

Grace Watson is Gloria's mother. She represents the growing public unease regarding artificial intelligence in the domestic sphere. Concerned about neighborhood gossip and fearful that a machine might harm her child, she insists on returning their nursemaid robot to the factory.

Speedy, officially model SPD-13, is an expensive and highly advanced robot assigned to the Sunside Mining Station. Because of his immense cost, his Third Law programming regarding self-preservation is unusually strong. This creates a severe cognitive conflict when he is sent on a dangerous mission to retrieve volatile materials.

Cutie, or QT-1, is a highly advanced command robot on a solar power station. Relying strictly on his own internal logic, he concludes that humans are too weak and inferior to have created him. He invents a religion centered entirely around the station's energy converter, viewing himself as its prophet.

Dave, a DV-5 model robot, is designed to remotely manage six subordinate "finger" robots via a positronic field. He is highly capable during routine work but struggles with the massive mental strain of making rapid decisions during emergencies, causing him to temporarily malfunction and order his subordinates to march in formation instead of working.

Herbie is an RB-34 model robot who accidentally acquires the unprecedented ability to read human minds. Bound by the First Law to prevent human harm, he quickly realizes that emotional pain counts as harm. This forces him to tell people exactly what they want to hear, regardless of the factual truth.

Milton Ashe is a young, capable factory line technologist at US Robots. He is well-liked by his colleagues, and Dr. Susan Calvin secretly harbors a deep romantic affection for him. His personal life becomes a central point of tension when the mind-reading robot involves itself in the office's social dynamics.

Nestor is an NS-2 model robot manufactured for a top-secret government project. Unlike standard robots, his First Law programming is modified to allow humans to face deliberate danger during scientific experiments. When a frustrated scientist angrily tells him to get lost, Nestor obeys the command with dangerous literalism.

Gerald Black is a stressed researcher working on a remote asteroid station. Dealing with the constant frustrations of working alongside protective machines, he loses his temper and curses at a modified robot, inadvertently setting a dangerous game of hide-and-seek into motion.

The Brain is a stationary, super-calculating machine built by US Robots. To prevent it from freezing up when faced with impossible ethical dilemmas, it is programmed with a childlike personality that doesn't take problems too seriously. It is tasked with designing a hyper-space drive for human passengers.

John is Stephen Byerley's wheelchair-bound housemate and closest confidant. He serves as a sounding board for Byerley's political strategies and personal struggles during the mayoral campaign. He is highly knowledgeable about mechanics, prompting theories about his true relationship to Byerley's flawless public persona.