We’ve been discussing a bit about this in the Starship Troopers thread, but I think it deserves its own discussion. It’s sometimes claimed that all of Heinlein’s works have only three characters in them, those being Young Heinlein, Adult Heinlein, Old Heinlein, and Virginia (I somehow suspect that the originator of the claim didn’t know how to count). While this is certainly not true (there are way more characters than that in Heinlein’s books), he nonetheless did have a tendency to reuse some characters with different names. The archetypes I can think of off the top of my head:
1: The Boy Scout. Hero of most of the juvies, he’s trustworthy, loyal, helpful, friendly, and all the rest. He may or may not be an official member of a Scouting organization, but the qualities are the same. It’s no coincidence that many of these characters debuted in Boy’s Life magazine. Prominent examples include Bill Lermer (Farmer in the Sky) and Matt Dodson (Space Cadet).
2: The Jokester. Another younger character. Won’t let you down in a pinch, but refuses to ever take anything seriously. Never the protagonist, but often shows up as the Boy Scout’s wisecracking sidekick. Such characters show up in Space Cadet, Tunnel in the Sky, and Red Planet, among others (though I can’t remember their names off the top of my head).
3: The Spoiled Brat. A minor antagonist, who shows up in many different ages but only one maturity level. Believes that the world owes him (or her; the Spoiled Brat can be either sex) a living, and refuses to accept the math that shows why what they want isn’t possible. The FN bureaucrats in The Moon is a Harsh Mistress and the colonists who give up on Ganymede in Farmer in the Sky are examples.
4: The Scamp. Another youth, and usually a protagonist, but unlike the Boy Scout, doesn’t play by the rules, and in fact seems to delight in chaos for its own sake. Is likely to eventually grow into an Old Fart, if not hanged for horse-thieving first. Examples include young Hazel from The Moon is a Harsh Mistress, Pollux and Castor from The Rolling Stones, and young Woody from Time Enough for Love.
5: The Old Fart. Older than dirt, and just as dirty. Has Been There and Done That, and is probably still Doing It (whatever It is). Always has a trick or two up his or her sleeve, and is generally regarded as a Bad Influence. Lazarus Long (Time Enough for Love and Grandmother Hazel (The Rolling Stones are the most prominent examples, as well as Lazarus’ grandfather.
6: The Engineer. Skilled with machines, and probably more comfortable with them than with humans. Always willing to face the facts, whatever the facts are. Seldom takes the lead in social situations, but takes things as they come. The most prominent examples are Manny in The Moon is a Harsh Mistress and D. B. Davis in The Door into Summer.
7: The Pedant. Well-educated and in a respected position, this character has extensive views on politics and the Way Things Should Be, and is willing to spend several pages expounding on those views (whatever they may be). Usually an old man, but in at least one case (in the short story “Coventry”), a teenaged girl. Other examples include Jubal Harshaw (Stranger in a Strange Land), Prof. del la Paz (The Moon is a Harsh Mistress), and Sgt. Zim (Starship Troopers).
8: The Alien Princess. Might easily be mistaken for a pet of the main human characters, but is actually a young member of some significant standing from a far more advanced race, and views the humans as pets. Has an immature, fun-loving worldview, and despite being referred to as “he” by the humans, is its species’ equivalent of a female, and talks with a girlish voice. Lummox (The Star Beast) and Willis (Red Planet) fit this archetype to a T, and Mike (The Moon is a Harsh Mistress) also shows some of the same characteristics.
I’m sure others can think of many more, and then there’s still plenty of Heinlein characters who don’t really have any equivalents (such as D. D. Harriman and Andy Libby).