What I know is that Cthulhu was created by H.P. Lovecraft not as a villain, but as a constant threat, sort of a looming, impending dread, like sitting next to an active time bomb with no clock face. He isn't so much a god as an unknowable being of a reality separate from ours, as is the case with all of the Great Old Ones.
As for the people who say that they've read the Necronomicon, there is NO SUCH THING. Lovecraft created the idea of the book the same way he created Cthulhu. Would-be demonologists and whatnot have usurped the name to create a "real" Necronomicon, but it's a complete work of fiction, as verified by his correspondence to William Conover.
Repeat, THERE IS NO REAL NECRONOMICON. Christ.
Okay, off my soap box now. Best Lovecraft stories:
The Music of Erich Zann
The Rats in the Walls
The Outsider
The Call of Cthulhu
The Colour Out of Space
The Dunwich Horror
The Shadow over Innsmouth
At the Mountains of Madness