Mrs. K, or Ylla
- The third-person narrator calls her Mrs. K; her husband calls her Ylla. She is a housewife on Mars. Her situation is much like that of the American housewife of the 1950s. She and her husband are tired of one another. She dreams of Captain Nathaniel York coming down in his rocket.
Mr. K, or Yll
- The husband of Ylla, Yll is suspicious of her dreams. He is practical and short-tempered.
- The captain of the first expedition, he appears only in Ylla's dreams, as a seductive, handsome man, but he is mentioned throughout the novel.
"The Earth Men"
- Williams is a clever man, the leader of the second expedition. He quickly realizes that he and his three men have been placed in an insane asylum.
"The Third Expedition"
Captain John Black
- Black is the leader of the third expedition. When his rocket lands in a quaint American town, he is very suspicious, but his men convince him to explore. He is charmed to see his family, but guesses that it is a trick, although he is too late.
- Hinkston is archaeologist for the third expedition. He eagerly makes up grand, if implausible, explanations for the American town in the middle of Mars. He is eighty, but is still spry due to future technologies.
"--And the Moon be Still as Bright"
- Wilder is a good leader, the captain of the fourth expedition. He wants to let his men relax and have a party, yet he understands why Spender wishes they would be more dignified. He half-agrees with Spender, and after his death tries to help preserve Mars. For this reason, Parkhill thinks, Wilder is sent off to explore Jupiter and Pluto. He returns to a desolated Mars, where he finds Hathaway living with a family of robots.
- Spender is the archaeologist for the fourth expedition. He reveres Mars and quickly leaves the crew to explore the planet by himself. He learns to read Martian. Finally, he decides that he should kill off the crew in an effort to preserve Mars. He kills several, including Cheroke, but doesn't have the heart to finish. He speaks for a long time to Wilder of how impossible it will be to protect Mars from government and corporate interests.
- A member of the fourth expedition, Parkhill is the opposite of Spender. He is eager to conquer the Martian landscape. He enjoys shooting out the windows of Martian ruins, for which Captain Wilder knocks out his teeth. After settlement begins in earnest, he leaves the military and opens a hot dog stand just in time for Mars to be evacuated. He is a violent, careless man.
- Hathaway is physician and geologist for the fourth expedition. He and his family do not leave Mars when the war starts on Earth. When the rest of his family dies and he is completely alone, he builds robot replicas of his dead family members.
- A member of the fourth expedition, Biggs is eager to party. Spender hates him.
- A member of the fourth expedition, Cheroke is of Cherokee descent. He claims to sympathize with the Martians, but he still stands up to Spender.
"The Green Morning"
- Driscoll is a simple man. He comes to Mars to be a laborer, but almost has to return because the oxygen is too thin for him. As a result, he decides to plant trees all over Mars to create oxygen.
- Gomez is an early settler. He is poetic when he thinks to himself, and he has a winning smile that he uses to greet Muhe Ca.
- A martian that Gomez meets, Muhe Ca seems to be from the past, but may simply be from another plane or dimension. He is friendly and has a deep love for the sort of festival he describes to Gomez.
Pop, or the old man
- This is an old man working at a gas station where Gomez stops. He believes that people should take Mars as it is and appreciate it for being different.
"Way in the Middle of the Air"
- A racist white storeowner, Mr. Teece sometimes participates in lynchings. He is shocked that the Negroes plan to leave. He tries to stop them with contracts and owed money, but his friends persuade him to let them go.
- Belter owes Mr. Teece fifty dollars. Other Negroes group together to pay off the debt.
- Silly works in Teece's store. He is a young man, but he hopes to start his own hardware store on Mars. Mr. Teece almost does not let him go because he has signed a contract to work for a certain period of time, but the other white men force Teece to let him go.
- A very rich man, Stendahl is a lover of fantasy authors like Edgar Allan Poe, Nathaniel Hawthorne, H. P. Lovecraft, and Lewis Carroll. These authors are banned on Earth, and his library is destroyed. He is bitter.
- Garrett is an Investigator of Moral Climates. He sends a robot replica of himself to investigate the house, Usher, which Stendahl has built. Later, he arrives himself and is shocked at what he finds.
- Pikes is Stendahl's partner in crime. He used to be an actor in fantasy movies--Stendahl compares him to Lon Chaney--now he is a master craftsman of robots.
- Tom is not actually Tom. That is, the real Tom is the deceased son of LaFarge and Anna. However, a Martian assumes the shape of Tom and wants to be accepted by the elderly couple. It craves love and is terrified of going to town.
LaFarge and Anna
- LaFarge is an old man. He and his wife Anna have moved to Mars to retire. They miss their son Tom, who died of pneumonia as a boy. When the Martian Tom arrives, LaFarge quickly guesses the truth, but he doesn't want to tell his wife, as it would hurt her deeply.
"The Off Season"
- Elma is the wife of Sam Parkhill. She is smarter than him and seems quietly amused at his mishandling of life on Mars.
"The Silent Towns"
- Walter Gripp lives in the mountains and does not realize that Mars has been evacuated because of the war on Earth. He is a simple, polite man. He desperately wants a female companion.
- Genevieve is a large woman. She eats constantly and seems childishly impatient and immature when with Walter.
"The Long Years"
- Williamson is part of the crew that Wilder took to Jupiter and Pluto. He goes to investigate whether Hathaway's real family might be dead.
"The Million-Year Picnic"
- The father of the family featured in this story is quiet, warm, and eager to start a completely new life on Mars. He burns a map of Earth, symbolizing his willingness to forget a past life. He is a former governor of Minnesota.
- Timothy is Dad's eldest son; he seems to be around thirteen years old. He takes his responsibility as example-setter to his younger brothers very seriously. He understands that there is something "strange" about this picnic on Mars, and he is automatically willing to help his father make it easier for his brothers.