Dr. Robert Laing is a 30-year-old doctor who teaches at a medical school located across the river from the development. Following a divorce, he moves to the 25th floor of the Brutalist high-rise seeking solitude and anonymity. He prefers the privacy of his apartment and maintains a detached, bohemian demeanor compared to his highly conformist neighbors. He adapts easily to the building's hostile environment, finding himself drawn into the territorial disputes of his floor.

Richard Wilder is a rugged former rugby player turned television documentarian who lives on the second floor with his family. He possesses a strong physical presence that contrasts with the mannered, unphysical bourgeois residents living above him. He resents the building's rigid social hierarchy, particularly the privileges afforded to the top floors, and plans to shoot a documentary exposing the realities of high-rise life.

Anthony Royal is the wealthy architect of the development who occupies the 40th-floor penthouse. After surviving a serious car crash, he walks with a chromium cane and wears a white safari jacket. He views the building as an ongoing social experiment, frequently observing the lower floors with detached fascination while walking his purebred white Alsatian dog.

Alice is Dr. Robert Laing's sister. She lives on a lower floor in the same high-rise and initially recommended the building to him. She serves as his primary family connection, visiting his apartment to seek assistance when the building's services begin to fail.

Charlotte Melville is a resident living directly above Dr. Robert Laing on the 26th floor. She actively participates in the petty disputes that define the building's early social dynamics. She hosts rowdy parties and questions Laing about the behavior of the upper-floor tenants, quickly drawing him into her orbit.

Helen Wilder is Richard Wilder's wife and mother to his two sons. She struggles with the building's frequent mechanical failures and feels physically oppressed by the massive concrete structure above her. She frequently begs her husband to secure an apartment on a higher floor or leave the building entirely.

Anne Royal is Anthony Royal's wife and the daughter of a wealthy industrialist. She relies on the technological conveniences of the penthouse to maintain her sense of class superiority. She becomes increasingly anxious about the deteriorating social decorum and demands they move out, though she struggles to actually leave.

Jane Sheridan is an actress living on the 37th floor. Her position in the upper levels makes her a target for lower-floor residents looking to elevate their social standing. She associates closely with the building's elite tenants and adapts quickly to the shifting loyalties of the top floors.

Dr. Steele is an oral surgeon who lives next door to Dr. Robert Laing on the 25th floor. He represents the highly adapted, unemotional high-rise tenant. He actively blames residents on other floors for the building's blocked garbage chutes and electrical failures, preferring to attack his neighbors rather than fault the architecture.

Mrs. Steele is Dr. Steele's wife. She shares her husband's detached approach to life in the building. She thrives in the rapid turnover of acquaintances, preferring superficial interactions over deep involvement with her neighbors.

Paul Crosland is a television newsreader living in the middle section of the building. He maintains a highly organized demeanor and serves as an informal leader for the 24th through 26th floors during early supply runs. He acts exactly as he does on television, bringing a broadcast-style authority to hallway disputes.

Adrian Talbot is a psychiatrist living on the 27th floor. He observes the growing tensions with academic interest, openly welcoming the exaggerated animosity among the tenants as a release from their constrained suburban routines. He actively theorizes about the psychological benefits of the building's breakdown.

Dr. Pangbourne is a top-floor gynecologist who relies on computerized data rather than traditional medical interaction. He acts as a key figure among the upper-echelon residents, quickly organizing them when floor-based conflicts arise. He studies recorded birth cries with intense fascination.

Eleanor Powell is a film critic living in the building. She recognizes the social deprivation inherent in the building's sterile environment and embraces the chaotic energy that begins to fracture the residents' strict routines. She frequently treats real-life events as if she is adjusting a television screen.

Mr. Hillman is a 17th-floor resident whose apartment serves as a base camp for lower-floor incursions. He suffers a severe injury during the early skirmishes, leaving him largely passive and unresponsive while others utilize his home for their own operations.

Mrs. Hillman is a 17th-floor resident who fortifies her apartment against intruders. With her husband injured, she relies on outside help for supplies and harbors deep resentment against the upper-floor residents. She arms herself to protect her home but hesitates to use lethal force.