In his essay "H. P. Lovecraft and the Cthulhu Mythos",
Robert M. Price described two stages in the development of the Cthulhu Mythos. Price called the first stage the "Cthulhu Mythos proper." This stage was formulated during Lovecraft's lifetime and was subject to his guidance. The second stage was guided by August Derleth who, in addition to publishing Lovecraft's stories after his death, attempted to categorize and expand the Mythos.
An ongoing theme in Lovecraft's work is the complete irrelevance of mankind in the face of the cosmic horrors that apparently exist in the universe.Great Old Ones", a loose pantheon of ancient, powerful
deities from space who once ruled the Earth and have since fallen into a deathlike sleep.
:viii While these monstrous deities have been present in almost all of Lovecraft's published work (his second short story
Dagon is considered the start of the mythos), the first story to really expand the pantheon of Great Old Ones and its themes is
The Call of Cthulhu, which was published in 1928.
Lovecraft made frequent references to the "
Lovecraft broke with other pulp writers of the time by having his main characters' minds deteriorate when afforded a glimpse of what exists outside their perceived reality. He emphasized the point by stating in the opening sentence of the story that "The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents."
Dirk W. Mosig notes that Lovecraft was a "mechanistic materialist" who embraced the philosophy of
cosmic indifference. Lovecraft believed in a purposeless, mechanical, and uncaring universe. Human beings, with their limited faculties, can never fully understand this universe, and the
cognitive dissonance caused by this revelation leads to insanity, in his view. This perspective made no allowance for religious belief which could not be supported scientifically, with the incomprehensible, cosmic forces of his tales having as little regard for humanity as humans have for insects.
There have been attempts at categorizing this fictional group of beings. Phillip A. Schreffler argues that by carefully scrutinizing Lovecraft's writings, a workable framework emerges that outlines the entire "pantheon"—from the unreachable "Outer Ones" (e.g.
Azathoth, who occupies the centre of the universe) and "Great Old Ones" (e.g. Cthulhu, imprisoned on Earth in the sunken city of
R'lyeh) to the lesser castes (the lowly slave
shoggoths and the
David E. Schultz, however, believes that Lovecraft never meant to create a canonical Mythos but rather intended his imaginary pantheon to merely serve as a background element.
:46, 54 Lovecraft himself humorously referred to his Mythos as "Yog Sothothery" (Dirk W Mosig coincidentally suggested the term Yog-Sothoth Cycle of Myth be substituted for Cthulhu Mythos).
 At times, Lovecraft even had to remind his readers that his Mythos creations were entirely fictional.
The view that there was no rigid structure is expounded upon by
S. T. Joshi, who said "Lovecraft's imaginary
cosmogony was never a static system but rather a sort of aesthetic construct that remained ever adaptable to its creator's developing personality and altering interests. . . . There was never a rigid system that might be posthumously appropriated. . . . The essence of the mythos lies not in a pantheon of imaginary deities nor in a cobwebby collection of forgotten tomes, but rather in a certain convincing cosmic attitude."
Price, however, believed that Lovecraft's writings could at least be divided into categories and identified three distinct themes: the "Dunsanian" (written a similar style as
Lord Dunsany), "Arkham" (occurring in Lovecraft's fictionalized
New England setting), and "Cthulhu" (the cosmic tales) cycles.
:9 Writer Will Murray noted that while Lovecraft often used his fictional pantheon in the stories he ghostwrote for other authors, he reserved Arkham and its environs exclusively for those tales he wrote under his own name.
Although the Mythos was not formalized or acknowledged between them, Lovecraft did correspond and share story elements with other contemporary writers including
Clark Ashton Smith,
Robert E. Howard,
Frank Belknap Long,
Henry S. Whitehead, and
Fritz Leiber—a group referred to as the "
For example, Robert E. Howard's character
Friedrich Von Junzt reads Lovecraft's
Necronomicon in the short story "The Children of the Night" (
1931), and in turn Lovecraft mentions Howard's
Unaussprechlichen Kulten in the stories "Out of the Aeons" (
1935) and "The Shadow Out of Time" (
:6–7 Many of Howard's original unedited
Conan stories also involve parts of the Cthulhu Mythos.
Price denotes the second stage's commencement with August Derleth. The principal difference between Lovecraft and Derleth being Derleth's use of hope and development of the idea that the Cthulhu mythos essentially represented a struggle between good and evil.
:9 Derleth is credited with creating the "Elder Gods." He stated:
As Lovecraft conceived the deities or forces of his mythos, there were, initially, the Elder Gods . . . These Elder Gods were benign deities, representing the forces of good, and existed peacefully . . . very rarely stirring forth to intervene in the unceasing struggle between the powers of evil and the
races of Earth. These powers of evil were variously known as the Great Old Ones or the Ancient Ones...
Price believes that the basis for Derleth's system is found in Lovecraft: "Was Derleth's use of the rubric 'Elder Gods' so alien to Lovecraft's in At the Mountains of Madness? Perhaps not. In fact, this very story, along with some hints from "The Shadow over Innsmouth", provides the key to the origin of the 'Derleth Mythos'. For in At the Mountains of Madness is shown the history of a conflict between interstellar races, first among them the Elder Ones and the Cthulhu-spawn.
Derleth himself believed that Lovecraft wished for other authors to actively write about the Mythos as opposed to it being a discrete plot device within Lovecraft's own stories.
:46–7 Derleth expanded the boundaries of the Mythos by including any passing reference to another author's story elements by Lovecraft as part of the genre. Just as Lovecraft made passing reference to Clark Ashton Smith's
Book of Eibon, Derleth in turn added Smith's
Ubbo-Sathla to the Mythos.
Derleth also attempted to connect the deities of the Mythos to the
four elements ("air", "earth", "fire", and "water"), creating new beings representative of certain elements in order to legitimize his system of classification. Derleth created "Cthugha" as a sort of fire elemental when a fan, Francis Towner Laney, complained that he had neglected to include the element in his schema. Laney, the editor of
The Acolyte, had categorized the Mythos in an essay that first appeared in the Winter 1942 issue of the magazine. Impressed by the glossary, Derleth asked Laney to rewrite it for publication in the Arkham House collection Beyond the Wall of Sleep (
 Laney's essay ("The Cthulhu Mythos") was later republished in Crypt of Cthulhu #32 (1985). In applying the elemental theory to beings that function on a cosmic scale (e.g.
Yog-Sothoth) some authors created a fifth element that they termed aethyr.