Must differ with you there, Toothill. Though REH and HPL did garner much of their fame after their early deaths, JRRT (I'm drowning in initials here) was very well-known while he was still alive.
The Hobbit did fairly well when released in the '30s, and LotR gained steam steadily from its first printing in the early '50s. It was a contentious book, to be sure, with most reviewers either loving it or, more commonly, hating it.
LotR really picked up in the '60s, and was quite well known by the time JRRT left us in the '70s.
Of course, you can say that each man's work was of sufficient quality that the man's fame only grew after death, which would be true. More succinctly, my point is that Tolkien (unlike the others) was not toiling in relative obscurity for the last two decades of his life.