Robert Anson Heinlein was one of the genuine gods of the genre. It is impossible to overstate or exaggerate his impact and effect on the medium. A huge number of the people my age (about 40!) or younger admit that Heinlein's stories are what turned them on to science fiction, or science. He is responsible for many "firsts" in science fiction that are now common staples of the trade, such as the multi-generation starship.
He was not without his quirks or clinkers. But they were a low percentage of his prodigious output. And there are those who think his work deteriorated in his later years. However, for a stinging refutation of that charge, and many others concerning him, find an article by Spider Robinson called "Rah, Rah, R.A.H.". The left-wing, long-haired hippy writes a scathing apologetic on the right-wing, short-haired old dude.
In a unique tribute just before he died, Larry Niven wrote an alternate time-track short story where the whole plot revolved around Senator William Proxmire's attempt to alter history by changing Heinlein's life to short-circuit the space program! (Not to kill him, but to cure him of a condition he had that cashiered him from the Navy, thus keeping him in the military and presumably preventing his writing career.)