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.