D-503 is the dedicated chief builder of the interstellar rocket, the Integral. Living in the authoritarian society of the One State a millennium in the future, he fully supports the mathematically perfect, heavily regulated life mandated by the government. He possesses "ape-like" hands and a highly logical mind that processes the world through mathematical formulas and geometric metaphors. His commitment to rationality faces an abrupt challenge when he encounters a woman who defies the established rules.

I-330 is an enigmatic citizen of the One State who wears illegal twentieth-century clothing and drinks alcohol. She operates outside the strict behavioral confines of the "Hour Tables" and treats the state's rigid regulations with a mix of amusement and contempt. Sharp, alluring, and rebellious, she uses her charm and knowledge of the forbidden past to draw others into subversive activities.

O-90 is a citizen assigned as a sexual partner to both D-503 and the poet R-13. She is ten centimeters shorter than the state's Maternal Norm, meaning the government legally bans her from bearing children. She embraces the comfortable routine of her assigned visits but retains an appreciation for the natural world, occasionally bringing flowers from the Botanical Garden. She displays genuine affection for her assigned partners despite the state's insistence on emotional detachment.

The Benefactor is the authoritarian leader of the One State. He presides over the society as a supreme, metallic figure with massive, cast-iron hands. The government demands universal adulation for him, staging annual "Day of Unanimity" elections where citizens publicly and harmoniously vote for his continued rule. He enforces mathematical happiness at the expense of individual freedom.

R-13 is an official state poet who composes verses celebrating executions and the mathematical perfection of the government. He has prominent lips and a boisterous personality that occasionally borders on the erratic. As D-503's former classmate, he shares a friendly history with the protagonist, though their interactions become strained by unacknowledged emotional complexities.

U- is an older woman who serves as the controller in D-503's block of transparent flats. She observes the daily activities of the residents and ensures their compliance with the One State's rigorous schedules. She maintains a stern, authoritative presence while also taking a specific interest in the residents she monitors.

S-4711 is a member of the Guardians, the One State's secret police force responsible for identifying and eliminating transgressions. He trails citizens to ensure absolute conformity to the "Hour Tables" and the Benefactor's laws. He possesses a double-curved posture resembling the letter S, making his physical form match his status as a watcher.

The Doctor is a physician at the Medical Bureau who examines citizens exhibiting signs of psychological or emotional distress. He operates within the state's highly clinical medical system but uses his position to issue falsified illness certificates. He observes the psychological shifts in his patients as the ordered society begins to crack.