H. P. Lovecraft created a number of fictional deities throughout the course of his literary career, including the "Great Old Ones" and the "Outer Gods", with sporadic references to other miscellaneous deities (e.g. Nodens) whereas the "Elder Things" are a later creation of other prolific writers such as August Derleth, who was credited with formalizing the Cthulhu Mythos.
As it is known in the mythos, the Outer Gods are ruled by Azathoth, the "Blind Idiot God", who holds court at the center of the universe. A group of Outer Gods dance rhythmically around Azathoth, in cadence to the piping of a demonic flute. Among the Outer Gods present at Azathoth's court are the entities called "Ultimate Gods" in The Dream-Quest of Unknown Kadath (called Lesser Outer Gods in the Call of Cthulhu RPG), and possibly Shub-Niggurath, the "Black Goat of the Woods". Yog-Sothoth, the "All-in-One", co-rules with Azathoth and exists as the incarnation of time in the cosmos, yet is somehow locked outside the mundane universe. Nyarlathotep, the "Crawling Chaos", is the of the Outer Gods, existing as the incarnation of space and functions as an intermediary between the deities of the pantheon and their cults. The only Outer God to have a true personality, Nyarlathotep possesses a malign intellect and reveals a mocking contempt for his masters.
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, with Lovecraft constantly referring to the "Great Old Ones": a loose pantheon of ancient, powerful deities from space who once ruled the Earth and who have since fallen into a deathlike sleep.
Lovecraft named several of these deities, including Cthulhu, Ghatanothoa, and Yig. With a few exceptions, Cthulhu, Ghatanothoa, et al., this loose pantheon apparently exists 'outside' of normal space-time. Though worshipped by deranged human (and inhuman) cults, these beings are generally imprisoned or restricted in their ability to interact with most people (beneath the sea, inside the Earth, in other dimensions, and so on), at least until the hapless protagonist is unwittingly exposed to them. Lovecraft visited this premise in many of his stories, notably his 1928 short story, The Call of Cthulhu, with reference to the eponymous creature. However, it was Derleth who applied the notion to all of the Great Old Ones. The majority of these have physical forms that the human mind is incapable of processing; simply viewing them renders the viewer incurably insane.