Harry Purvis is a regular at the White Hart pub who frequently shares elaborate tall tales with the patrons. Described as an unreliable narrator with questionable academic credentials, he serves as the storyteller for several of the book's humorous narratives. He spins accounts of unusual scientific phenomena and odd individuals, entertaining his fellow drinkers while keeping them guessing about the truth of his words.

Senator Steelman is an ambitious American politician working in the capital. After dedicating his life to pursuing power and preparing for a potential presidential run, he discovers he has a serious heart condition that limits his time. This medical diagnosis prompts him to reevaluate his strained family relationships and his past political decisions regarding astrobiology funding.

Bertrond is an explorer and scientist with the Galactic Survey. Journeying through space in search of intelligent life, he carries the heavy burden of knowing his own civilization faces an imminent threat. He is deeply curious and remarkably patient, taking the time to study and interact with early human-like civilizations on a fertile new planet.

The Jesuit Priest serves as an astrophysicist and the chief scientist aboard an exploratory vessel. He travels to the debris of the Phoenix Nebula to investigate the aftermath of a supernova. As a deeply religious man of science, his discoveries force him to confront severe philosophical questions regarding divine will and universal justice.

Dr. Bill Cross is a frustrated and bitter rocket engineer who designs missiles instead of the spaceships he dreams of building. Dealing with recent professional rejections and romantic failures, he turns to alcohol to cope. His heavily intoxicated state leaves him particularly unreceptive when an extraterrestrial intelligence attempts to contact him.

The Dog-Owning Scientist is an astronomer who prioritizes his career in space exploration over personal connections. He isolates himself emotionally from others, believing that his line of work requires strict detachment. His professional distance is challenged when he adopts a stray puppy that alters his perspective on companionship.

Hercules Keating is a diminutive and socially isolated man who prefers the company of his plants over people. Deeply resentful of his domineering relative, he immerses himself in botany as an escape. Upon acquiring a rare, carnivorous orchid, he begins to entertain dark fantasies about using the plant to solve his familial frustrations.

Shervane is a young, curious resident of a planet illuminated by a single, stationary sun. Inheriting immense wealth after the sudden death of his father, he becomes fixated on an impenetrable black barrier known as the Wall. He dedicates his adult life and resources to financing an expedition to cross the structure and see what lies beyond.

Dr. Wagner is an American computer scientist who supplies advanced technology to a remote Tibetan monastery. Pragmatic and business-oriented, he facilitates the transportation of the machine and assigns engineers to operate it. He completely dismisses the spiritual significance of the monks' endeavor, viewing it purely as a mechanical transaction.

The Lama is the spiritual leader of a Tibetan monastery who hires Western engineers. He oversees a massive undertaking to list all the true names of a divine entity, believing that completing this task will fulfill the ultimate purpose of the human race. He remains calm and unwavering in his faith.

Arthur C. Clarke appears as a fictionalized version of the author, reflecting on his time as a Royal Air Force radar operator. He attends diplomatic parties and worries that his early scientific concepts regarding satellite communication are being weaponized. He observes these technological shifts with a growing sense of dread.

Gene Hartford is a clean-cut American working with foreign powers to establish a global satellite communications system. He operates under the guise of producing educational content while actively planning to broadcast tantalizing and morally questionable material to manipulate viewers.

Alveron is the captain of the S9000, an intergalactic rescue ship dispatched by a superhuman alien race. He leads an urgent mission to evacuate humans from Earth hours before the sun detonates. He remains genuinely concerned for the fate of humanity despite assuming they possess drastically inferior technology.

Collin Sherard is an astronaut who crashes his space-pod onto the surface of an asteroid destined to collide with the sun. Trapped and facing extreme temperatures, he attempts to drag his crippled vessel toward safety while contemplating the human drive for discovery and the unforgiving nature of space.

Marvin is a ten-year-old boy living in an isolated colony on a distant planet. Having never stepped outside his shelter, he takes a significant journey across the rugged terrain to see the radioactive ruins of his ancestral home. He carries the heavy expectation of preserving human history.

Georges is a research assistant who recognizes the commercial potential of a machine capable of recording and transmitting physical sensations. Driven by greed and ambition, he begins recording intense sensory experiences to market to wealthy consumers, severely neglecting his personal life in the process.

Laika is an intelligent dog rescued as an abandoned puppy. She grows from a destructive youth into an attentive and highly intuitive companion. She forms an intense, protective attachment to her owner, possessing highly sensitive instincts regarding natural disasters.

Aunt Henrietta is Hercules Keating's towering, cigar-smoking relative. She breeds large dogs and routinely subjects her nephew to weekly visits. Brash and patronizing, she remains entirely oblivious to the intense resentment her nephew harbors toward her overbearing personality.

Brayldon is an older boy who befriends Shervane and shares his fascination with the edge of their known world. He grows up to become a highly skilled architect, bringing essential technical expertise to Shervane's ambitious construction project at the Wall.

Grayle is an elderly philosopher and tutor who educates the youth of his world. He provides crucial context about the nature of the universe and attempts to explain complex theoretical concepts using simple physical models involving paper loops.

Chuck is an engineer assigned to maintain a sequence computer in Tibet. He is deeply uncomfortable with the remote assignment and the monks' apocalyptic beliefs. Preferring earthly comforts, he plans a speedy departure before the project finishes to avoid any potential backlash.

Rugon is the Deputy Captain aboard the S9000 rescue ship. Analytical and highly observant, he questions the initial assumptions his crew makes regarding human behavior. He pushes his captain to investigate mysterious transmission beams, suspecting the humans might be more capable than initially thought.

Yaan is a member of an early human settlement on a fertile planet. He encounters strange visitors who offer him food and tools. Approaching the strangers with a mix of caution and reverence, he struggles to comprehend their true nature and origins, viewing them as divine figures.

Marvin's Father is a survivor living in an off-world colony. He takes his son on a crucial expedition to witness the radioactive remains of Earth, passing down the history of their civilization. He bears the emotional weight of a long exile from his home planet.

Yvette is the girlfriend of a distracted research assistant. She becomes increasingly alienated and suspicious of her partner's erratic behavior and constant use of sensory recording equipment. Her frustration mounts as she feels utterly ignored in her relationship.

Dr. Harkness is a scientist and former political rival of a powerful senator. Previously mocked as "Hapless Harkness" for his poor public speaking and ambitious space research proposals, he returns years later to deliver vital news regarding advanced medical treatments developed overseas.

Irene is the daughter of a prominent Washington politician. She facilitates visits between her father and his grandchildren, providing him with a grounding sense of family during a difficult personal transition. She serves as a vital emotional link for a man who previously ignored his personal life.

Clindar is a researcher traveling alongside Bertrond. He utilizes a robotic suit to safely explore hostile planetary environments and provide security during first-contact scenarios. He monitors local wildlife and stands ready to protect his colleagues.