[from archives; originally from April 2006, so Google results may vary]
Three authors dominated post-WWII science fiction: Robert Heinlein, Isaac Asimov, and Arthur C. Clarke. They weren’t necessarily everyone’s favorite authors, but they were the ones that had to be acknowledged, and often they were the intro to the field for the new reader / neo-fan. And the general consensus has stood the test of time; these three are still among the most famous science fiction writers. A quick Google search shows 6.5, 11, and 14 million hits, respectively for the three, with only Philip K. Dick (14 million) and Ray Bradbury (8.4 million) as equivalents in fame.
(For reference: Tolkien gets 26 million Google hits, Rowling gets 25 million, Hemingway gets 22 million, and Hunter S. Thompson gets 24 million. Shakespeare manages 122 million, and I’m guessing he’s the writer standard. To be more famous than Shakespeare, you have to either have a major religion – Jesus gets 280 million hits – or be the father of your country – Washington gets 2.6 billion hits. Founding a minor religion does help, however; L. Ron Hubbard gets 5 million hits, and it isn’t because of Typewriter in the Sky).
So why these guys and not, for example, Fritz Leiber, Henry Kuttner, or Ray Bradbury? Kuttner, of course, died young, which was career limiting in his case. Lieber was as much a fantasist as science fiction writer, though he did publish in Astounding on occasion, just not frequently enough. The Astounding factor was even more apparent with Bradbury. Not to put too fine a point on it, but Bradbury may have been the favorite SF writer of school teachers and Bugs Bunny, but he didn’t publish in Astounding, and that was that.
Asimov, Heinlein, and Clarke, on the other hand were science fiction writers. Even on those rare occasions when one of them wrote fantasy, it read like science fiction (e.g. "Magic Incorporated"). Nevertheless, they filled different ecological niches.
Heinlein is the easiest of the three to categorize, at least in terms of what he offered to the core audience of upwardly mobile bright guys. Heinlein offered the personal and political philosophy of the competent man. His authorial voice was pedantic in the best sense; readers got the feeling that they were learning something from his expository asides, and the antagonists in his stories were the same small-minded ignorant people that his readers dealt with (or at least thought they dealt with) every day.
Clarke was the mystic and transcendentalist, as befits one strongly influenced by Olaf Stapleton. In reviewing a list of Clarke’s short stories, I was stuck by just how often Clarke wrote about the end of the world, from his first story, “Rescue Party”, to the tongue-in-cheek “Nine Billion Names of God,” to the novel Childhood’s End, Clarke seemed to delight in just doing away with it all.
Yet, at the same time, Clarke’s science fiction offered immortality and transcendence. In Childhood’s End, humanity merged into a group mind and left the planet (destroying it in the process). In The City and the Stars, the citizens live for a thousand years, “die” and are then reborn with a set of edited memories, a technological reincarnation, with hints of karmic justice tossed in. In 2001, the Childhood’s End scenario runs again, only this time for a single individual, and the Earth is still around at the end of the book (though its fate is in apotheotic hands.
What Clarke offered to the intent reader, therefore, was science fiction as an alternative to the faith-of-our-fathers. You get all the elements of fundamentalist Christianity (eternal life, apocalyptic visions, God-like vistas), but with faith in technology as the underpinning, rather than just faith alone.
So what about Asimov? He was obviously the Secular Humanist of the trio, with the additional attraction of the “I am one of you” persona. He made no secret of his fanhood; indeed, he gloried in it. Then, when he decided to embark upon another career as a popularizer of science, he did so in essays that were accessible, personal, and fun. His readers came away with not just knowledge, but the belief that they’d like to have dinner with Issac, and, moreover, that they could have dinner with Isaac, given a bit of luck. And they were right, because Isaac in person was pretty much the same as Isaac on the page, educated, garrulous, witty, erudite. He was many a fan’s image of his own ideal self, the nerd as hail-fellow-well-met.
Following the establishment of the science fiction ecology, the niches were bound to be further carved up and refined. The entire genre of “military science fiction” owes most of its existence to Heinlein’s Starship Troopers, as does “libertarian science fiction” (and libertarianism generally) owe to The Moon is a Harsh Mistress. In the 1960s, Harlan Ellison became Lenny Bruce to Asimov’s Henny Youngman, using the personal essay as an adjunct to a fiction career, while others noticed that there might be a market for science writing, if done appealingly. And if Heinlein’s Destination Moon gave a boost to any kid who wanted to work for the space program, Clarke/Kubrick’s 2001: A Space Odyssey gave notice to a whole generation of dopers that space might be really trippy, even if you didn’t actually go there.