Harley Warren is a mysterious occultist who appears in H. P. Lovecraft's story "The Statement of Randolph Carter" as a friend of Carter (in the dream the story was based on Samuel Loveman was the Warren character). He apparently perishes while exploring an underground crypt in Big Cypress Swamp, leaving Carter above, unharmed but mentally shaken. Warren is also mentioned in another Lovecraft story, "The Silver Key", as "a man in the south, who was shunned and feared for the blaspemous things he read in prehistoric books and clay tablets smuggled from India and Arabia" as well as "Through the Gates of the Silver Key" in which he was revealed to have been an expert linguist of the primal Naacal language of the Himalayas.
What singles Warren out from Lovecraft's many other doomed characters is his self-sacrificial, gentle nature (he pleads with Carter to put back the crypt's slab and run for it while he still has the chance) combined with a sinister element that is more in keeping with Lovecraft's other ambiguous anti-heroes such as Pickman and Herbert West (Carter describes Warren's expression as disquieting when he talks of his occult theories).
What really caused Warren's death down there in the underground swamp crypt is unknown; in a letter that Lovecraft wrote to Clark Ashton Smith, he mentions that Warren may have been destroyed by a 'begetting entity' within Smith's tale The Nameless Offspring, but this is quite possibly more speculation between friends than actual fact.
A character who bears a resemblance to him is Clark Ashton Smith's antehuman sorcerer Haon-Dor (from "The Seven Geases"), another seeker after forbidden lore. Warren is also mentioned in Brian Lumley's Titus Crow series as a member of a Bostonian group of psychics.
Several actors in cinematic renditions of The Statement of Randolph Carter have portrayed Harley Warren, the most notable of them being John Rhys-Davies in The Unnamable II: The Statement of Randolph Carter.
The H.P. Lovecraft Historical society did a song entitled "Harley got devoured by the undead", a parody of "Grandma got Ran over by a Reindeer".