"The Call of Cthulhu," by H.P. Lovecraft, is presented as the posthumous account of the narrator's discovery of a giant undersea monster and the cult that worships it. Papers and artifacts left by a relative lead him to discover multiple groups of cultists throughout the world, and the evidence ultimately leads him to an uncharted island that is home to the terrifying creature.
While H.P. Lovecraft wrote a large number of eldritch horror stories and never considered "The Call of Cthulhu" to be one of his best, the story proved to be the most enduring of his career. The universe he created through his stories is often referred to simply as the "Cthulhu Mythos," and it has been adapted in other books, movies and even games.
"The Call of Cthulhu" follows a familiar pattern in Lovecraft's works. The narrator of the story discovers something odd through chance, and while investigating the peculiarity he stumbles across a conspiracy of those who worship ancient horrors from beyond space and time. Ultimately, a confrontation with the monsters or gods usually results in the death or insanity of everyone involved. The bleak tone of the story, which centers around humanity discovering a malevolent force it has no hope of defeating, is one of the trademark aspects of Lovecraft's writing style.