Dr. Kris Kelvin is a psychologist and dedicated researcher who has spent 12 years studying the living ocean of Solaris through historical texts. Arriving at the space station to work with his mentor, he finds the facility in a state of chaos and decay. He carries heavy emotional baggage, particularly the guilt surrounding the tragic suicide of his 19-year-old wife a decade prior. He is observant and emotionally driven, relying on his psychological training to investigate the bizarre phenomena manifesting on the station.

Rheya/Harey appears on the space station as an exact, 19-year-old replica of Kris's late wife, wearing the same dress from the day she died. As a physical manifestation created by the living ocean of Solaris, she is indistinguishable from a human on the surface but possesses unique physiological traits, such as blood made of neutrinos and rapid healing capabilities. She initially believes herself to be the original woman, complete with deep affection for Kris, but soon experiences severe confusion regarding her true nature and sudden existence.

Dr. Snow is the space station's older, gaunt cyber technician. He is highly logical and serves as a pragmatic counterpart to Kris's emotional reactions. Deeply scarred by recent events on the station, he initially offers only cryptic warnings about the environment. He hides his own mysterious visitor and attempts to maintain a detached, scientific approach to an impossible and horrifying situation.

Dr. Sartorius is the space station's withdrawn and untrusting nuclear physicist. He is intensely private, hiding his own mysterious visitor behind locked doors, and focuses entirely on finding a technological solution to the station's ongoing crisis. Pompous and rigid in his thinking, he prioritizes the destruction of the ocean's manifestations over understanding them, causing friction with Kris's empathetic approach.

Dr. Gibarian is a longtime researcher whose drive to establish direct communication with the living ocean led him to conduct unauthorized radiation experiments. Though he takes his own life before Kris arrives at the station, his presence lingers through his chaotic quarters, his recorded messages, and the mysterious woman who continually visits his remains. He serves as a cautionary figure regarding the consequences of scientific obsession.

Berton is a helicopter pilot who survived a harrowing accident during the early expeditions on the planet Solaris. He provides vital eyewitness testimony about the ocean's ability to create massive, complex structures. His accounts are largely dismissed by authorities as hallucinations, illustrating the scientific community's resistance to unexplainable phenomena.

Dr. Messenger is a member of the review council tasked with evaluating early exploration incidents on Solaris. Unlike his rigid peers who dismiss unusual findings as impossible, he demonstrates a willingness to listen to eyewitness accounts. He sits with Berton to hear the full extent of his experiences with the living ocean.