system
Given the following post, respond as if you're commenting on Reddit:
human
[Lovecraft] How does Cthulu fit into the wider Lovecraftian universe?

As in he is the Gatekeeper in "Call of Cthulu" for the Elder Gods but his role changes as Lovecraft wrote more books... or something.
gpt
Cthulhu, like Nyarlathothep, Yog-Sothoth and the others, is an Elder God. Elder Gods are immortal alien beings, only partly comprised of matter as we understand it and unimaginably powerful. They see humanity, inasmuch as they "think" of us at all, as you would see a small anthill in your garden - vaguely interesting little pests who have no way of understanding how powerful you are or what you want.

The only reason why they haven't destroyed us utterly yet is that they're sleeping - hence the Cthulhu Cult invocation "Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn", meaning roughly "In his house at R'lyeh dead Cthulhu waits dreaming".

Now, some cults have attempted to build a kind of "mythology" around the Elders, giving them roles - Cthulhu as a kind of water elemental, H-stur as its air counterpart, Yog-Sothoth as "The Door And The Key", Nyarlathothep as a sort of Satan-like being (makes deals, changes his physical form, etc), Shub-Niggurath (the Goat with a Thousand Young) as a fertility divinity, etc. These attempts, however, reflect mainly the views of the cultists/hermetists and should be taken with a grain of salt.

For more information, the Miskatonic University library might be able to help - Dr. Armitage is always most helpful to the true scholar. 

Further reading: 

L. Shrewsbury, *An Investigation into Myth-Patterns of Latter-Day Primitives* and *Cthulhu in the Necronomicon* (unfin., post.)

Dr. M. A. Murray, *The Witch-Cult in Western Europe*

F. von Junzt, *Unaussprechlichen Kulten*


Primary sources: 

A. Alrhazed, *Necronomicon*

anon., *Liber Ivonis*

anon., *Pnakotic Manuscripts*