Valentine Michael Smith is born on Mars to Earthling parents who die almost immediately after his birth, and is raised by the Martian race. Thus, his experience is entirely unique. He is unlike any other Martian because of his human physiology, and unlike any other human beings because of his Martian ways of thought. Mental powers that human beings assume are impossible, such as telekinesis and mind reading, are second nature to him, and his philosophies are entirely Martian as well—for example, if a "water-brother" (a close companion) wished him to will his body to die, Mike would be delighted to comply. Earth customs such as jealousy, desire, and lying are utterly foreign to him, implying that these qualities which often seem inherent to the human condition are learned.
Although Mike would seem to be the novel's central character—he is the titular stranger in a strange land—his journey toward understanding his human roots occurs largely in the margins of the plot. Instead, Heinlein focuses on Mike's companions' reactions to his growth. Therefore, Mike's leaps in "grokking" humankind often seem to occur quite precipitously. Under Jubal's tutelage he learns about the structure of human society; from his murderous encounter with Digby he learns self-reliance; from his days in the carnival he learns the value of showmanship; and from his days in Las Vegas he learns the nature of desire. From watching monkeys at the zoo he has the final revelation that makes him fully human. He learns that comedy and tragedy are inextricably intertwined, and that people laugh to soothe the pain of the horrors they have created for themselves. Mike weaves all of his knowledge, Martian and Earthling, into the Church of All Worlds, his noble attempt to help humankind rise above suffering.
It has been suggested by many critics that the irrepressible Jubal Harshaw, rather than Mike, is the main character of the novel. Certainly Jubal occupies center stage more often than any other character, and so much of the novel is devoting to his espousal of individualist ideologies as to make his worldview seem intractably central to the novel's philosophy. Not every character always agrees with Jubal, but none ever presents a substantive counterargument to his assertions—even Mike, who flummoxes Jubal with his religious pursuits, always defers to Jubal and weaves Jubal's teachings into his own. What Jubal presents as a contention that every person is responsible for taking control of his or her own destiny, Mike reinterprets as "Thou art God!" The centrality of Jubal's belief system to the story, combined with the obvious parallels of their writing careers, has led many critics to believe that Jubal is a stand-in for Robert A. Heinlein himself.
Jubal also would seem to fit the mold of protagonist considering how he learns and changes during the story, though this change occurs not gradually but almost entirely in the last part of the novel. He has been a rock solid source of wisdom for the other characters, and he believes himself too old to alter his ways. His self-imposed celibacy is a symbol that he is now more observer than participant in the ongoing human comedy. In developing a fatherly attachment to Mike, Jubal reopens himself to emotions that he has shut off. Jubal does have actual grown children of his own, but they are not a presence in his life or his thoughts. Perhaps with Mike he is getting a unexpected second chance at fatherhood, a role for which he had been too busy earlier in life. When Mike gets into trouble, Jubal's fatherly instincts cause him to rush to Mike's side. There, he is genuinely unnerved by the cultish aspects of Mike's church, and he finds himself warming to their ways. At novel's end, after Mike's death, Jubal seems poised to carry on Mike's work. Though Jubal has been acutely aware of the faults in organized institutions, his love for Mike and his followers has opened him to the possibility of spreading Martian gospel.
Jill begins the novel as a nurse, a professional nurturer. When she meets Mike, though he is not ill, he is in need of a guide and a protector, and Jill fills these roles comfortably. She is not shy about her sexuality and in the very first sentence she appears in tells us that "her hobby was men," so she is also a fine teacher for Mike's education in the bipolarity of the human sexes, which Mike ultimately comes to regard as humankind's greatest gift. She is the first woman Mike ever sees, the first woman he shares water with, and the first woman he kisses. She may or may not be the woman to whom Mike loses his virginity—the identity of that woman is left ambiguous. As such, there is a deep bond between them that remains until the end of the novel, even when Mike has taken on many other water-brothers and lovers. It is her compassionate attachment to Mike, borne of their first encounter, which leads her to stick close to him, and grow and change with him throughout their journeys. Though Jill begins sexually liberal, Mike's penchant for constant nudity and eventually group sex require her to broaden her horizons further—steps that she would only take alongside Mike, whom she trusts absolutely. Though Ben is fixated upon her and wants a traditional marriage with her, he senses that her compassion for Mike is too deep for him to be able to compete.
The summary incorrectly states that Apollo is the Greek "word" for Mars. Actually, Ares is the Greek name for the god known as Mars in Latin.
Apollo is one of the few classical gods known by nearly the same name in Greek and Latin. In English, he is called Apollo in both contexts.