Ooookay. Quick literary lesson here, the short version with most of the details left out:
When Lovecraft died in 1936, he should have plummeted into the same literary obscurity as guys like Seabury Quinn, another popular *Weird Tales * writer. Most pulp writers simply never broke through into the mainstream, and most people today have never heard of the majority of 'em.
Due largely to two men – Donald Wandrei and August Derleth – Lovecraft is still in print. They founded Arkham House Publishing, a small press devoted to *Weird Tales * anthologies and reprints of Lovecraft stuff. Over time, both Arkham House and Lovecraft’s material developed a cult following.
Derleth obtained much of Lovecraft’s unfinished paperwork and manuscripts, and finished several stories that Lovecraft did not. He also reworked some of Lovecraft’s notes into complete stories. He published these works as “posthumous collaborations” under the authorship of “H.P. Lovecraft and August Derleth.”
When he ran out of Lovecraft notes and ephemera, he continued to write Mythos fiction, and continued to stick Lovecraft’s name on it in front of his own; some of his last “collaborations” were limited to a quote from an existing Lovecraft book or story at the beginning of the book!
…so is this bad? Well, Derleth wasn’t a bad writer, but he wasn’t Lovecraft. Most Lovecraft freaks will tell you that Derleth’s stuff wasn’t as good as the original.
Derleth was largely responsible for hammering together the “Cthulhu Mythos,” and he was certainly responsible for keeping all this stuff in print. This is good. On the other hand, rather than leave most of the cosmic stuff all vague and unstated, he tended to want to quantify and explain things, and turn the vague and horrifying conflicts of the Old Ones and the Elder Gods into a good-vs.-evil shootin’ match, which would have irritated Lovecraft to no end; his gods and monsters didn’t know “good and evil” from “dog doodle and Shinola,” and couldn’t have cared less. Hell, one of his more benign creatures thought they were doing people a favor by sticking their brains in jars and taking them on a tour of the universe…
Confusing the issue even further is the question of Lovecraft’s “revisions.” Y’see, Lovecraft ghosted a fair number of stories for various people. He ghosted one story for Harry Houdini, because the editor of Weird Tales wanted to cash in on his friendship with Houdini and that person’s very-well-publicized return from a vacation in Egypt, and he paid Lovecraft to ghost the story which would be published as “Imprisoned With The Pharaohs, by Harry Houdini.”
Other persons, notably Hazel Heald and C. J. Eddy, paid Lovecraft to revise and edit their material so’s they could get into print and be Published Authors, even if it was in the horror pulps. From what I understand, Heald’s stuff was so wretched that Lovecraft pretty much rewrote her stories from stem to stern, and therefore her stories that he ghosted… he pretty much wrote from scratch, perhaps with a germ of an idea provided by the patron. Other stories were anything from collaborations to mere editing jobs; the facts are unclear. At any rate, most of Lovecraft’s revisions are available in two paperback editions, The Loved Dead and The Horror In The Museum; both are quite worthwhile for Lovecraft buffs.
…but if you’re lookin’ for the pure stuff, check the book. If Derleth’s name is on the cover, you’re lookin’ at a “posthumous collaboration.” Caveat Emptor, and all that.