Lovecraftian & The Cthulhu Mythos
Plenty of authors can claim that their works have been subject to the blessing (or curse) of fan fiction. Sometimes the demand is so high, or the draw so strong, that professional authors take up the challenge. Occasionally, the descriptor fan fiction seems alien and derisive to a collection of such works. With the Cthulhu Mythos however, fan fiction is simply wrong. The Cthulhu Mythos (works based on or derived from the works of H.P. Lovecraft) is a unique development within literature. Hundreds of stories have been written picking up where HPL left off, filling in the gaps or simply using the strange array of creatures and locations HPL devised for their own means and exploration. Many of the earliest stories in the canon were written whilst HPL was still alive, and he and his cohort would discuss the various elements at great length, including Clark Ashton Smith, Fritz Leiber and Frank Belknap Long. August Derleth progressed the Mythos even further through Arkham house and academics, such as S.T. Joshi, have helped formalise the endeavour. There is plenty of wind left in the sails though, and stories continue to this day.
Lovecraftian Horror is, of course, related, but not necessarily within the same shared space; Lovecraftian Horror is distinct from the Cthulhu Mythos as it relies less on the actual characters and locales, and more on the eerie feel and cosmic nature of stories.