Ironically, it was during this time that HPL was doing the bulk of his professionally published revision work, much of it no less than actual ghostwriting. Lovecraft might provide a nearly complete text of a story based on a few root ideas supplied by the "author". Stories such as Zealia Bishop's "The Curse of Yig" and "The Mound", and Hazel Heald's "The Horror in the Museum" and "Out of the Aeons" were in fact 90% or more the product of H.P. Lovecraft. While these stories were quickly accepted by Wright, Lovecraft's work under his own name continued to be rejected.

The practice of trading deities, books, and themes from one writer's stories to another was in full swing at this time, and Lovecraft seemed to join in the game with his revision tales. Bishop's two stories are set in the American southwest and here we find Lovecraft's Cthulhu and Smith's Tsathoggua, along with the introduction of Yig. All three are worshiped by a heretofore unguessed-at race of subterranean humans. "Out of the Aeons" introduces a new deity, Ghatanothoa, described through the vehicle of Robert E. Howard's Nameless Cults and linking both to Lovecraft's own fungi from Yuggoth. "The Horror in the Museum" introduces us to dimensional shamblers and a Great Old One known as Rhan-Tegoth.

The 1940s and '50s saw a quiet expansion of the Mythos. Robert Bloch and James Wade added a few stories to the canon, but it was August Derleth who contributed the most, producing a number of original tales as well as posthumous collaborations based on Lovecraft's story notes. It was not until 1964 that the appearance of a young Britisher named Ramsey Campbell heralded a renewed interest in the Cthulhu Mythos.

Encouraged by August Derleth, Campbell's first published collection, The Inhabitant of the Lake and Other Less Welcome Tenants (1964), was a series of Lovecraft-inspired pastiches set in England's Severn Valley. These stories described a number of different beings, races, and histories similar to, but distinct from Lovecraft's. His most famous Mythos creations include Y'golonac, Glaaki, the insects from Shagghai, and a host of other creatures and god-like beings (see Made In Goatswood). 1971 saw the emergence of another Britisher, Brian Lumley, who brought to the Mythos the underground chthonians, the mysterious G'harne Fragments, and the modern-day sorcerer Titus Crow (see Singers of Strange Songs).

Numerous other contemporary contributors directly influenced by Lovecraft include Gary Myers, Basil Copper, T.E.D. Klein, David Drake, and Thomas Ligotti. Many others, such as Stephen King, have made special contributions to anthologies of new Mythos tales. Few writers of modern horror fiction can claim there is no Lovecraft influence in their work.

Lovecraft died in near obscurity in March of 1937, at the age of 46 a victim of Bright's disease and virulent cancer. His mother had died in 1921 after two years' confinement in the same institution where his father had died. A brief, two-year marriage accompanied by residence in New York proved disastrous, though divorce was never made final, and in 1926 Lovecraft had fled home to Providence to live out his years a bachelor, sharing quarters with two aunts. These last years saw a reduced output of fiction but it was during this period that he produced some of his most memorable tales. He also found time to travel, visiting places that tickled his antiquarian heart: Maine, Philadelphia, Quebec, St. Augustine, Charlotte, New Orleans, Salem, and Nantucket. Traveling by bus, sleeping in YMCAs, and eating crackers, cheese, and canned beans, Lovecraft was able to indulge his personal tastes for the old, the antique, and the decaying.
Plenty of evidence exists to show that Lovecraft was, by any assessment, an odd individual. Predisposed to hypochondria and a premature pose of old age, for much of his life he was committed to social and artistic views more suitable to centuries past than the one he lived in. Allergic to cold and repulsed by seafood, he was also a scientist and a philosopher possessed of an inquiring mind and sharp wit. Most who came to know him during his lifetime were left profoundly changed by his friendship. Encouraged and enlightened by his erudition and no-nonsense philosophies, many went on to achieve fame far greater than their mentor ever enjoyed during his lifetime. He has the same effect today, generations after his death. His name is better known than ever and those who discover him, whether through his stories, through films, games, comics, or trading cards, find themselves as fascinated by his bizarre creations and nightmare worlds as were his contemporaries so many years ago.