To answer Joben's question a little more directly:
H(oward). P(hillips). Lovecraft was an American horror writer of the 1920's and early 30's. One of his major inspirations was Edgar Allan Poe, and Lovecraft's work in turn was an inspiration for Stephen King.
Most of his work was in the form of short stories and novellas, which have been collected into several books. You should be able to find them in most libraries and bookstores. My favorite Lovecraft works, the ones that I think best evoke the flavor of the Cthulhu mythos, are "The Dunwich Horror", "At the Mountains of Madness", "Pickman's Model", "The Doom that Came to Sarnath", and of course the classic "Call of Cthulhu".
After Lovecraft's death, some of his editors and correspondents (most notably August Derleth) tried to patch up some of his unfinished manuscripts and write some more stories in the same vein. Also, there was a fairly strong Lovecraftian revival in the 1980's and 90's, and several authors wrote "Cthulhu mythos" stories of their own. None of these are as good as the original.