To call H.P. Lovecraft a jumble of contradictions would be, in short, putting it lightly: if the fact that one of the most significant contributors to the genre of horror fiction is also widely considered to be an awful writer doesn't encapsulate this, then little else does.
The paradoxes in Lovecraft's works — most notably the writer's Cthulhu Mythos, a shared universe that connects most of his fiction ruled by god or god-like creatures called the Old Ones (more on them later) — is almost considered a mainstay. Scientific inquiry leads his characters to discover the supernatural; an atheist author readily includes the existence of divine beings; humanist themes imbued in his writing came directly from a man whose rampant xenophobia and selective racism were considered highly vitriolic, even in his day.
Despite this, the incongruity that was H.P. Lovecraft as a person, as well as his complex grasp of the inner-workings of horror, is why his work has been tantamount to modern pop culture, found in everything from games to movies to books to TV. Below are some that wouldn't exist without H.P.L., and have changed the face of pop culture as we know it.
Psycho and Conan the Barbarian
It can't be said that Lovecraft's influence was as directly related to Psycho and the Conan the Barbarian series, which were originally written as novels by Robert Bloch and Robert E. Howard respectively. Both of the Roberts were part of what is now known as the Lovecraft Circle, a group of younger writers that HP mentored through a series of letter correspondences. The mutual literary impact that the members of the Circle had on each other can be best summed up by the incorporation of a grimoire — or a fictional book of magic — concocted by Bloch into the works of his fellow writers. Titled De Vermis Mysteriis, the imaginary tome first appeared in the Bloch 1935 short story "The Shambler from the Stars"; it later appeared in Lovecraft's Cthulhu lore, with Lovecraft himself giving Bloch a Latin incantation for the younger author to use in his works: "Tibi, magnum Innominandum, signa stellarum nigrarum et bufoniformis Sadoquae sigillum" ("To you, the great Not-to-Be-Named, signs of the black stars and the seal of the toad-shaped Tsathoggua"). This incantation also appeared the works of Clarke Ashton Smith, another Circle devotee.
While the older author's literary guidance might have turned both Psycho and Conan into the cultural hallmarks that they are, his imprint extends even further than the novels and stories the Circle wrote. One of the strangest examples? If it weren't for the movie adaptation of Conan, we might not have had The Terminator — the 1982 film is considered Arnold Schwarzenegger's acting breakthrough. As we all know, a world without a Governator joke is a world not worth living in.
Dungeons & Dragons
Lovecraft, a perpetual nitpick, had an almost unparalleled hatred of games. In a letter to anarchist writer James F. Morton, he denounced them as "by-products of excess intellectuality" for people of leisure with too much time on their hands, "simply avenues of escape for persons with too poorly proportioned and correlated a perspective to distinguish betwixt the frivolous and the relevant."
Like much of Lovecraftian fare, his work went on to inspire some of the most influential RPGs and video games out there — like Dungeons & Dragons.
Yes, it's true — if it weren't for Lovecraft, the most quintessential RPG of them all would have either been significantly altered from what we now know it to be, or maybe never even created at all. The 1979 first edition of Dungeon Masters Guide named Lovecraft, along with other greats like J.R.R. Tolkien, as one of the major models for the tabletop (specifically in Appendix N under the category "Inspirational Source Material"), and Gary Gygax, the designer behind the fantasy RPG, listed him among some of the game's biggest tastemakers, among them which included aforementioned Lovecraft mentee and Conan author Howard.
The Evil Dead Franchise
Considered one of the greatest entries in the comedy-horror genre, the Evil Dead movie franchise more or less owes its entire existence to Lovecraft, with the inclusion of another one of the author's grimoires, titled the Necronomicon. Concocted as yet another aspect of the Cthulhu Mythos, director Sam Raimi incorporated a version of the fictional compendium of dark magic in Evil Dead and Evil Dead 2 under a slightly altered title, the Necronomicon Ex-Mortis, which is more or less responsible for propelling the plot: the book is the tool in which the evil forces (i.e., "the Force") in the franchise's universe can be summoned, controlling both the dead and living servants known as "Deadites."
(On an unrelated note, the Necronomicon shows up in myriad other works of horror, but perhaps the strangest is the ninth entry of the Friday the 13th slasher franchise, titled Friday the 13th: Jason Goes to Hell. Even though it doesn't have as major significance in the movie as it does in Evil Dead and Evil Dead 2, its presence more or less connects both to H.P.'s Cthulhu folklore — meaning that you could pit all three in the exact same fictive universe).
Buffy the Vampire Slayer
When a show about an ex-cheerleader-turned-teenage-vampire killer starring Sarah Michelle Gellar premiered on the WB (what is now known as the CW) in 1997, not even its creator Joss Whedon could have predicted its cultural impact, from its reputation as the first show to usher in the golden age of television (Robert Moore from Popmatters said of the show "TV was not art before Buffy, but it was afterwards") to own a corner in academia known as Buffyology. However, who could have foretold that Lovecraft, a noted sexist, directly contributed to the creation of one of the greatest feminist icons in pop culture?
Lovecraft's cultural and narrative endowment to Buffy came in the form of "the Old Ones," a group of ancient deities known as the "Outer Gods" or "the Great Old Ones" in Lovecraft's Cthulhu universe. As malevolent as they are omnipresent, Buffy's Old Ones take their cues from Lovecraft's own; he described their role in his stories as a connector:
"... based on the fundamental lore or legend that this world was inhabited at one time by a race who, in practicing black magic, lost their foothold and were expelled, yet live on the outside ever ready to take possession of the earth again."
As many scholars have since noted, Lovecraft's words are echoed by Buffy's mentor Giles in the first season episode "The Harvest" when also describing the Old Ones:
"This world is older than any of you know. Contrary to popular mythology, it did not begin as a paradise. For untold eons demons walked the Earth. They made it their home, their ... their Hell. But in time, they lost their purchase on this reality. The way was made for mortal animals, for man. All that remains of the Old Ones are vestiges, certain magicks, certain creatures ..."
It should come as no surprise that 2012's comedy horror The Cabin in the Woods, written by Whedon and director Drew Goddard, also implemented Lovecraft's Old Ones into its storyline, instead naming them "Ancient Ones."