It’s H P Lovecraft’s 125th birthday! He is, I think, one of the most influential writers of the 20th century. He’s also in many ways a genuinely terrible writer. (I have an ongoing intermittent debate with Elizabeth Knox over whether he is the worst great writer or the greatest worst writer).
Unusually he’s influenced both pulp writers (too many to name) and literary writers (Borges, Cormac McCarthy, Houellebecq, Emmanuel Carrere). The pulp writers tend to borrow the trappings of his stories: the monsters, the cults, the forbidden books, but use them in conventional ways. What makes Lovecraft’s ‘cosmic horror’ effective is the existentialism; the cosmic insignificance of humanity, and that comes across in the literary influences. The Road and Blood Meridian are deeply Lovecraftian.
If you haven’t read any of his short stories then I recommend starting with The Call of Cthulhu.