Heinlein may have been the all-time most important writer of American Genre SF; along with H G Wells, who established the Scientific Romance as well as formulating in usable form many of sf's central tropes, he was not only an initial shaper of genre but the central maker of stories in the genre he had shaped.
and accepted today chronology and history of the ancient and medieval world, evidently contains big mistakes. NUMBERS AGAINST LIES (Contents, Foreword, Abstract) - A. For the next half a century he was the father – loved, resisted, emulated – of the dominant US form of the genre. Unlike most of John W Campbell Jr's pre-World War Two recruits to Astounding, he entered the field as a mature man, already in his thirties, with one genuine career (the military) honourably behind him.He was smart, aggressive, collegial, competent and highly inventive.In a style which exuded assurance and savvy, his early writing blended slang, folk aphorism, technical jargon, clever understatement, apparent casualness, a concentration on people rather than gadgets, and a sense that the world described was real; it was a kind of writing able to incorporate the great mass of necessary sf data necessary without recourse to the long descriptive passages and deadening explanations common to earlier sf, so that his stories spoke with a smoothness and authority which came to seem the very tone of things to come.His characters were competent men of action, equally at home with their fists and a slide-rule (see Edisonade) and actively involved in the processes and procedures (political, legal, military, industrial, etc.) which make the world turn.