Captain Wilder appears first in "June 2001: —and the Moon Be Still As Bright" as a moderate caught between radical Martian sympathizer Jeff Spender and the rest of his crew. He is eventually sent on a mission to the outer planets of the solar system so he does not interfere in government policy on Mars. He reappears on Mars in "April 2026: The Long Years" and eats breakfast with Hathaway more than 20 years after their original expedition; Wilder is presumed to have returned to Earth and died there. Because he tries to do what is right, he may be considered the moral center of the novel.
Jeff Spender appears only in "June 2001: —and the Moon Be Still As Bright" but he makes a lasting impression as a human who engages in cultural posturing, claiming Martian development is superior to that of humans (a claim the Martians themselves never make). However, he, unlike others in his crew, is sensitive and open-minded and willing to let Mars change his way of thinking. Unfortunately, he is too willing to accept change and reject the known. He takes his Martian sympathies to radical levels, becoming a terrorist and killing his own men. Instead of turning himself over, he forces Captain Wilder to kill him, making him a martyr for the Martians—a martyr they never asked for.
Hathaway appears in both "June 2001: —and the Moon Be Still As Bright" and "April 2026: The Long Years." He survives the fourth expedition, quits being a soldier, and settles down with his family who all die in 2007. He is so lonely that, in order to survive, he makes robots that resemble his family.
Sam Parkhill appears in both "June 2001: —and the Moon Be Still As Bright" and "The Off Season." He is coarse and rude and represents the less flattering characteristics of humankind. He eventually returns to Earth. His first name is the same as the racist Samuel Teece of "June 2003: Way in the Middle of the Air," equating him with one of the most narrow-minded of Bradbury's characters.