John is a perceptive writer who begins researching a historical account about the day the atomic bomb was dropped on Hiroshima. His investigation leads him into the lives of the Hoenikker family and eventually to the island nation of San Lorenzo. Initially a Christian with a jaded outlook on the world, he becomes increasingly fascinated by the local religion of Bokononism.

The late Dr. Hoenikker is the brilliant but emotionally detached scientist primarily responsible for developing the atomic bomb, later exploring the concept of a water-freezing isotope called ice-nine. He viewed scientific research as a playful exercise driven by pure curiosity, completely ignoring the moral or emotional implications of his work. His detached genius left a complicated legacy for both his family and the world.

Born Lionel Boyd Johnson in Tobago, Bokonon is the founder and central figure of Bokononism, a religion native to San Lorenzo. Despite the faith being officially outlawed by the government, he exerts tremendous influence over the island's inhabitants. He openly admits that his teachings are built on comforting lies designed to bring happiness to people trapped in difficult circumstances.

Newt is the youngest of the Hoenikker children, a little person who recently dropped out of college as a pre-med student. He is a frank, independent thinker and a passionate painter who creates a canvas depicting a cat's cradle. Unlike his older sister, he views his famous father critically and maintains a grounded perspective on his family's history.

Angela is the oldest Hoenikker child, who dropped out of high school to serve as a maternal figure for her family following her mother's death. She fiercely protects her father's reputation, viewing him as a great man despite his emotional neglect. She is also an exceptionally talented clarinetist, using music as an outlet for her underlying frustrations.

The middle Hoenikker child, Frank shares his father's technical mind and preference for distancing himself from people. As a youth in Ilium, he spent his time secretly building detailed models. He has since vanished and resurfaced as a military general and the minister of science for the island nation of San Lorenzo.

Miguel "Papa" Monzano is the aging, severe military dictator of San Lorenzo. He aligns his regime firmly with science and Christianity while aggressively enforcing the ban on Bokononism, utilizing the gruesome punishment of "the hook." Despite his powerful public persona, he suffers from rapidly declining health behind closed doors.

Mona is the incredibly beautiful adopted daughter of Papa Monzano, utilized heavily as a national symbol and political asset. A talented xylophone player, she quietly embraces Bokononism and its physical practices. She approaches relationships with a detached, universal love mandated by her secret faith, causing friction with suitors who desire exclusivity.

Dr. Breed is the highly articulate supervisor who oversaw Dr. Hoenikker's work at the General Forge and Foundry. He firmly believes in "pure research" and the unmitigated pursuit of scientific knowledge. He actively defends the scientific community against moral criticism and serves as a highly professional counterpart to the eccentric Dr. Hoenikker.

Marvin is Dr. Asa Breed's brother and a tombstone salesman in Ilium. Unlike his scientifically minded brother, Marvin is emotional and highly critical of the detached nature of scientists like Dr. Hoenikker. He harbors a long-standing resentment over the way Emily Hoenikker was treated during her life.

Julian is a former wealthy sugar magnate who abandoned his indulgent, selfish lifestyle at the age of forty. He now runs the House of Hope and Mercy, a free hospital in the jungles of San Lorenzo, dedicating his life to charitable works. He embraces a cynical, worldly perspective even as he serves the impoverished population.

Julian's son, Philip grew up in San Lorenzo and was personally tutored by Bokonon. He is the author of a semi-scholarly book about the island and owns the Casa Mona hotel, which he opened largely to combat his own loneliness. He maintains a sarcastic exterior and harbors unrequited feelings for Mona.

Lowe is an American industrialist traveling to San Lorenzo with hopes of relocating his bicycle manufacturing plant. He seeks an environment free of labor unions and high taxes. He is outspoken, staunchly patriotic, and highly supportive of strict disciplinary regimes like San Lorenzo's penal system.

Hazel is Lowe's wife and a fiercely proud native of Indiana. She insists on calling any fellow Indianan a "Hoosier" and demands they call her "Mom." She provides enthusiastic support for her husband's business ventures and remains trusting of authority and nationalistic pride.

Horlick is a thoughtful and mildly pessimistic career diplomat. He approaches foreign relations with a cosmopolitan outlook, sharply contrasting with the blind patriotism of other American travelers. He forms an exclusive, incredibly tight bond with his wife.

Claire is Horlick's wife and a former professional indexer. She is deeply observant and analytical, capable of discerning character traits simply by reading the index of a book. She previously derailed her husband's career by writing a brutally honest letter to the New York Times regarding foreign policy.

Emily was Dr. Felix Hoenikker's wife and the mother of his three children. She died as a result of an injury sustained while retrieving her husband's abandoned car, combined with childbirth complications. Her memory evokes strong protective feelings from her children and lingering affection from local men who knew her.

Harrison is a handsome former lab assistant to Dr. Hoenikker who has risen to become the president of a major munitions corporation. He married Angela Hoenikker shortly after her father's death.

Zinka is a Ukrainian dancer and a little person who engages in a brief, highly publicized romantic relationship with Newt Hoenikker before returning to the Soviet Union.

Earl is an intelligent Marine deserter who was shipwrecked on San Lorenzo alongside Bokonon in 1922. He became the island's ruler and co-created the dynamic between the government and the outlawed Bokononist religion in an attempt to provide the citizens with a comforting distraction from their poverty.

A medical doctor at the House of Hope and Mercy, he is a former Nazi SS officer who worked at a concentration camp. He now dedicates his life to trying to save patients in San Lorenzo as an impossible form of medical penance for his past actions.