Juliette is a 34-year-old, highly skilled mechanic who works in the deepest levels of the silo. Independent and practical, she harbors a deep hatred for disrepair stemming from a childhood tragedy involving her baby brother's death in a faulty incubator. Her exceptional mechanical talents and strong moral compass make her a prime candidate for leadership, though she initially prefers the familiar confines of the lower levels. She approaches problems logically and believes anything can be fixed with the right tools.

Bernard is the head of IT, a powerful department occupying the privileged upper levels of the silo. He is a staunch traditionalist who believes strict adherence to the silo's rules and class hierarchies is absolutely necessary to maintain order. Physically removed from the manual labor of the lower levels, he presents as a physically degenerated knowledge worker with small hands and a protruding gut. He acts as a pragmatic, sometimes ruthless leader willing to sacrifice individuals to ensure the survival of the entire population.

Lukas is a 25-year-old IT worker who spends his free time meticulously tracking the nighttime skies on the silo's screens. He is methodical and curious, yet he inherently respects the silo's rules and believes public order is necessary. His fascination with the outside world and his position within IT place him directly between the conflicting ideologies of his superiors and the people of the lower levels.

Marie Jahns is the contemplative, long-serving mayor of the silo. She feels the heavy burden of her leadership, acutely aware of the fragile balance of their underground society. Though she enforces the silo's strict laws, she privately harbors doubts about its rituals and views the cleaning executions as barbaric. She approaches her duties with a mix of political pragmatism and deep empathy for her citizens.

Holston is the respected sheriff of the silo who has spent the last three years grieving his wife's death. The burden of enforcing the silo's laws weighs heavily on him, especially as he becomes consumed by the same dangerous curiosity that led his wife to her execution. He is a methodical investigator whose personal tragedy drives him to question the fundamental nature of their enclosed world.

Marnes is the longtime deputy to the sheriff, a role he comfortably occupies without aspirations for the top position. He is a dependable and observant lawman who prefers to support from the shadows. His dedication to his work masks a deep, long-unspoken affection for the mayor, prioritizing propriety over his own happiness for many years.

Solo, whose real name is Jimmy, is an isolated survivor living in an abandoned, flooded silo. Traumatized by the horrific violence that destroyed his community when he was sixteen, he is deeply lonely, paranoid, and emotionally stunted. He survives by scavenging food and hiding in a secretive IT bunkroom, remaining mentally stuck in his teenage years.

Knox is the enormous, heavily bearded foreman of Mechanical. Despite his gruff and imposing exterior, he is a sensitive leader who feels a deep responsibility for the mechanics under his command. He is fiercely loyal to his department and harbors growing resentment toward the privileged upper levels of the silo, eventually finding himself thrust into a dangerous leadership role.

Walker is an elderly, highly introverted electronics specialist in Mechanical who has not left his workshop in four decades. He is wise but timid, relying entirely on others to bring him news and supplies. Despite his fears, his technical expertise and quiet acts of defiance play a crucial part in the mechanics' operations and communication efforts.

Peter is an ambitious young man shadowing to become a judge, but he is swiftly pushed into law enforcement by his sponsor in IT. He represents the middle-class aspirations of the silo, generally trusting the established order and relying heavily on the guidance of his superiors rather than questioning the system.

Shirly is a dedicated mechanic in the down deep who works closely with Juliette. She is caring and fiercely protective of her friends, taking it upon herself to look after the reclusive Walker. She demonstrates immense bravery and technical adaptability when pushed into dangerous circumstances.

McLain is the beloved leader of the Supply department. She is a small, elderly, white-haired woman who commands immense respect through her strategic thinking and imposing presence. She is a thorough planner who forces her allies to consider worst-case scenarios rather than rushing into impulsive action.

Allison is an intelligent and curious IT worker whose specialized skills allow her to uncover dangerous historical data hidden on the silo's servers. Her startling discoveries about past uprisings lead her to question the reality of their contained world, ultimately resulting in a public breakdown that sets the story in motion.

Scottie is a young IT worker who formerly shadowed in Mechanical under Walker. He maintains some loyalty to his old friends in the down deep but finds himself terrified by the implications of the secretive programs he works with in the upper levels.

Doctor Nichols is an imposing, emotionally reserved man who works in the silo's nursery. The trauma of losing his infant son and the subsequent suicide of his wife drove a permanent wedge between him and his daughter, leading to a decades-long estrangement.

Marck is a mechanic from the down deep. He is deeply devoted to his wife Shirly and demonstrates significant bravery and self-sacrifice during times of crisis, prioritizing the safety of his fellow mechanics over his own well-being.