H. P. Lovecraft

Howard Phillips Lovecraft (August 20, 1890 – March 15, 1937) was an American author of fantasy and horror fiction, whose work influenced Doom (and also Quake) significantly. In particular, Sandy Petersen is a big fan of Lovecraft.

Specific references include:
 * The name of the Cacodemon may have been taken from the sentence "I have said that the fury of the rushing blast was infernal - cacodaemoniacal - and that its voices were hideous with pent-up viciousness and desolate eternities." from The Nameless City