"[O]utside the ordered universe [is] that amorphous blight of nethermost confusion which blasphemes and bubbles at the center of all infinity—the boundless daemon sultan Azathoth, whose name no lips dare speak aloud, and who gnaws hungrily in inconceivable, unlighted chambers beyond time and space amidst the muffled, maddening beating of vile drums and the thin monotonous whine of accursed flutes."
~HPL, The Dream-Quest of Unknown Kadath~


Azathoth, sometimes called "The Blind Idiot God", the "Nuclear Chaos", the "Daemon Sultan", "The Deep Dark", and "The Cold One", is an Outer God.


Description
There can be no definite description of Azathoth because everybody envisions him differently and he is always changing. There is evidence the physical manifestation of Azathoth in the universe is continuous with a spot in the central region of the galaxy, otherwise known as Sagittarius A* - the supermassive black hole at the center of the Milky Way galaxy.

For example Ronald Shea enters a temple after visiting the forest near Goatswood and discovers a twenty-foot idol that "represented the god Azathoth--Azathoth as he had been before his exile. Outside, It consisted of a bivalvular shell supported on many pairs of flexible legs. From the half-open shell rose several jointed cylinders, tipped with polypous appendages; and in the darkness inside the shell I thought I saw a horrible bestial, mouthless face, with deep-sunk eyes and covered with glistening black hair."

Later Shae sees "something ooze into the corridor--a pale grey shape, expanding and crinkling, which glistened and shook gelatinously as still-moving particles dropped free; but it was only a glimpse" (EXP: "The Insects from Shaggai", Ramsey Campbell).

In the Necronomicon
zathoth is a significant malign presence In the Necronomicon as both Albert Wilmarth (HPL: "The Whisperer in Darkness") and Walter Gilman (HPL: "The Dreams in the Witch House") are horrified at the mere mention of its name having both read about it in the occult tome.

In Gilman's case it's the witch Keziah Mason who references Azathoth while haunting his dreams telling him "He must meet The Black Man, and go with them all to the throne of Azathoth at the centre of ultimate Chaos.... He must sign in his own blood the book of Azathoth and take a new secret name.... What kept him from going with her...to the throne of Chaos where the thin flutes pipe mindlessly was the fact that he had seen the name 'Azathoth' in the Necronomicon, and knew it stood for a primal horror too horrible for description."

It is also portrayed as a leader in a cosmic upheaval akin to Lucifer's rebellion in the Bible and is prophesied to return.

In the Mythos
Gilman wakes from another dream remembering "the thin, monotonous piping of an unseen flute", and decides that "he had picked up that last conception from what he had read in the Necronomicon about the mindless entity Azathoth, which rules all time and space from a curiously environed black throne at the centre of Chaos."He later fears finding himself in the spiral black vortices of that ultimate void of Chaos wherein reigns the mindless daemon-sultan Azathoth" (HPL: "The Dreams in the Witch House").

The poet Edward Pickman Derby wrote a collection of "nightmare lyrics" called "Azathoth and Other Horrors." (HPL: The Thing on the Doorstep).