James Holden is an idealistic former United Nations Naval officer from Earth who captains the stolen Martian corvette, the Rocinante. Raised in Montana by a collective of eight parents, he operates with a firm moral compass and an instinct to protect the vulnerable. These traits often put him at odds with political strategists who view him as a rogue operator. He currently works for the Outer Planets Alliance alongside a tight-knit crew he considers his found family.

Bobbie is a highly skilled gunnery sergeant in the Martian Marine Corps. A woman of Polynesian descent raised in Martian gravity, she takes intense pride in her custom-built Goliath III powered armor. Traumatized by the brutal slaughter of her elite squad on Ganymede, she struggles with grief while forced into diplomatic duties on Earth. Her military training gives her a straightforward approach to problem-solving that provides a clear contrast to Earth's political maneuvers.

Avasarala is the United Nations undersecretary of executive administration on Earth. She wields immense political influence behind a grandmotherly appearance. Of South Asian descent and favoring traditional saris, she uses an abrasive manner and frequent cursing to project strength and maintain control. She is a master strategist driven by a desire to prevent interplanetary war and protect the innocent, personally motivated by the tragic death of her teenage son.

Praxidike Meng is a mild-mannered botanist of East Asian descent working on the Jovian moon of Ganymede. He specializes in genetically engineering crops to sustain human life on the outer colonies. When his young daughter goes missing during a catastrophic attack on the station, he channels his scientific determination into an increasingly desperate search for her. His pursuit pulls him out of his academic comfort zone and onto the Rocinante.

Jules-Pierre Mao is an immensely wealthy and powerful corporate titan who heads Mao-Kwikowski Mercantile. His former company, Protogen, was responsible for unleashing the horrific protomolecule experiments on Eros. Despite his polite and humble outward demeanor, he represents unchecked corporate greed and a willingness to cross profound ethical boundaries.

Errinwright is the second-in-command at the United Nations, serving as the Secretary of Executive Administration. He represents the hawkish, technologically ambitious side of Earth's leadership. He prioritizes military supremacy over humanitarian concerns as the solar system edges closer to war.

Naomi is a Belter engineer and the highly intelligent executive officer of the Rocinante. She possesses multiple degrees but prefers the freedom of working aboard the ship. As the voice of calm and reason among the crew, she frequently reins in Holden's brash decision-making and advocates for teamwork over lone heroism.

Amos is the stoic, mechanically gifted mechanic of the Rocinante, originally from Earth. A large, physically intimidating man with a dark past, he constantly projects an aura of professional lethality. Despite his seeming sociopathy and capacity for violence, he possesses a strict moral compass and harbors a fierce instinct to protect children and vulnerable people.

Alex is the good-natured, easygoing Martian pilot of the Rocinante, hailing from the Mariner Valley. Pushing fifty and balding, he brings a relaxed Texas drawl and a calm demeanor to the high-stakes environment of the ship. He is highly observant, an excellent listener, and dedicated to the found family he has built with his crewmates.

Mei is the four-year-old daughter of Praxidike Meng. She suffers from a rare genetic disorder that disables her immune system, requiring regular medication. Her abduction from Ganymede serves as the catalyst for her father's desperate search and unites the crew of the Rocinante in their mission to rescue her.

Fred Johnson is the leader of the Outer Planets Alliance (OPA), a group striving to establish sovereignty for the Belt. An ex-Navy officer, he employs the crew of the Rocinante to investigate the strange occurrences on the Jovian moon. His access to the last known sample of the alien protomolecule makes him a subject of suspicion.

Dr. Strickland is a disgraced scientist formerly known as Carlos Merrian, who was fired for violating ethical boundaries. He acts as Mei's pediatrician on Ganymede but uses this position to monitor and eventually abduct immuno-compromised children for use in horrific biological experiments.

Admiral Nguyen is a young, self-important leader within the United Nations military who is eager to provoke a war with Mars. He commands a fleet of warships dispatched to Ganymede and prioritizes Earth's military dominance over interplanetary stability.

Soren is the political assistant to Chrisjen Avasarala at the United Nations. He is tasked with handling sensitive intelligence and managing routine tasks within the high-stakes environment of Earth's executive administration.

Arjun is Chrisjen Avasarala's husband, providing a calming presence distinct from the cutthroat world of Earth's politics. He acts as her emotional anchor and confidant, helping her maintain her humanity and moral clarity amidst her stressful responsibilities.

Admiral Souther is a high-ranking military officer within the United Nations fleet who maintains a sense of integrity and basic decency. He becomes a crucial ally to Avasarala in her efforts to prevent an all-out interplanetary war.

Captain Thorsson is an intelligence officer on Ganymede who is skeptical of Bobbie's reports regarding the monstrous humanoid. He is more concerned with protocol and career preservation than uncovering the truth behind the massacre.

Captain Martens is a Martian military chaplain who attempts to help Bobbie process the trauma of losing her entire squad. He represents the military's psychological support system, though his methods often clash with Bobbie's need for direct action.

Basia is a resident of Ganymede and a friend of Prax whose son, Katoa, suffers from the same immune disorder as Mei. Devastated by the colony's collapse, he decides to evacuate his remaining family rather than continue the seemingly hopeless search.

Nicola is Praxidike Meng's ex-wife and Mei's mother. She left the family due to her dissatisfaction with life on Ganymede, creating a deep emotional rift between her and Prax, which complicates the desperate search for their daughter.

Cotyar is the head of Chrisjen Avasarala's personal security detail. He is a capable and highly trained professional who assists Bobbie in preparing for tactical engagements while surviving the dangerous political environment of space transit.

Larson is a United Nations sailor who survives the initial protomolecule hybrid attack on his ship by hiding in a locker. Terrified but dutiful, he assists Holden in navigating the infected vessel to secure critical command codes.

Katoa is the young son of Basia who suffers from the same immune system deficiency as Mei Meng. He is kidnapped from Ganymede by Dr. Strickland as part of the horrific biological experiments.

Detective Joe Miller is Holden's deceased former partner who sacrificed his life to steer the infected Eros Station into Venus. Though physically dead, his memory heavily influences Holden's psychological state.

Julie Mao is the deceased daughter of corporate titan Jules-Pierre Mao. Her rebellion against her family and subsequent death as patient zero on Eros Station continue to cast a shadow over her father's brutal scientific ambitions.