Heinlein reportedly named his main character "Smith" because of a speech he made at a science fiction convention regarding the unpronounceable names assigned to extraterrestrials. After describing the importance of establishing a dramatic difference between humans and aliens, Heinlein concluded, "Besides, whoever heard of a Martian named Smith?" ("A Martian Named Smith" was both Heinlein's working title for the book and the name of the screenplay started by Harshaw at the end). The title Stranger In a Strange Land is taken from Exodus 2:22, "And she bore him a son, and he called his name Gershom: for he said, I have been a stranger in a strange land".
In the preface for the re-issued book, Virginia Heinlein writes: "The given names of the chief characters have great importance to the plot. They were carefully selected: Jubal means 'the father of all,' Michael stands for 'Who is like God?'".
- Valentine Michael Smith — known as Michael Smith or "Mike"; the "Man from Mars", raised on Mars in the interval between the landing of his parents' ship, the Envoy , and arrival of the second expedition, the Champion ; about 20 years old when the Champion arrives and brings him to Earth.
- Gillian (Jill) Boardman — a nurse at Bethesda Hospital who sneaks Mike out of government custody; she plays a key role in introducing him to human culture and becomes one of his closest confidantes, becoming a central figure in the Church of All Worlds which Mike develops.
- Ben Caxton — an early love interest of Jill, and an investigative journalist (Jill sees him as of the lippmann" or, political, rather than the "winchell", or celebrity gossip inclination), who masterminds Mike's initial freedom from custody, and ; he joins Mike's inner circle but remains somewhat skeptical at first of the social order it develops.
- Jubal Harshaw — popular writer, lawyer, and doctor, now semi-retired to a house in the Pocono Mountains; as an influential but reclusive public figure, he provides pivotal support for Mike's independence and a safe haven for him; elderly but in good health, he serves as a father figure for the inner circle while keeping a suspicious distance from it.
- Anne, Miriam, Dorcas — Harshaw's three personal/professional secretaries, who live with him and take turns as "front" responding to his instructions; Anne is certified as a Fair Witness, empowered to provide objective legal testimony about events she witnesses; they become early acolytes of Michael's church.
- Duke, Larry – Handymen who work for Harshaw, living in his estate; also become central members of the church.
- Dr. "Stinky" Mahmoud — semanticist, the second human (after Mike) to gain a working knowledge of the Martian language, though he does not "grok" the language; becomes a member of the church while retaining his Muslim faith.
- Patty Paiwonski – a "tattooed lady" and snake handler at the circus Mike and Jill join for a time, with ties to the Fosterite church, which she retains as a member of Mike's inner circle.
- Joseph Douglas — Secretary-General of the Federation of Free States, which has evolved indirectly from the United Nations into a true world government.
- Alice Douglas — (sometimes called "Agnes"), wife of Joe Douglas. As the First Lady, she manipulates her husband, making major economic, political, and staffing decisions. She frequently consults astrologer Becky Vesant for major decisions.
- Foster — founder of the Church of the New Revelation (Fosterite); now existing as an archangel.
- Digby — Foster's successor as head of the Fosterite Church; becomes an archangel under Foster after his "discorporation" by Mike.
