Bel-Shamharoth
Bel-Shamharoth (also known as the "Soul-Eater," the "Soul-Render," or the "Sender of Eight") is an ancient, dark god for whom the description "evil" is inappropriate; "negative" and "void" might be better terms. Bel-Shamharoth is all suckers, tentacles, mandibles, and one giant eye. His dilapidated temple is built of two-to-the-power-three-sided stones, with 7a sided tiles, lit in an eerie dark violet and possibly octarine light by twice-four-sided crystals, and a number of main corridors one more than seven and one less than nine leads to the center of the temple, where there is a slab with the same number of sides as a spider has legs. Rincewind, unwillingly visiting the temple, has likened it to a spider's web. In addition to leading the visitors to the center, whichever way they may turn, the temple also is bigger on the inside than the outside, a quality often found in buildings that do not occupy real space-time. The temple and Bel-Shamharoth himself appear in The Colour of Magic. The temple is long since abandoned, worship of the Sender of Eight being a decidedly short term prospect. These days he is mostly remembered in the name of the Young Men's Reformed Cultists of the Ichor God Bel-Shamharoth Association (which is also known as the Young Men's Pagan Association or YMPA). His likeness is etched on the cover of the Octavo.
It has been speculated that Bel-Shamharoth is a Creature from the Dungeon Dimensions who has managed to cling onto the Discworld and gathered worshippers (see The Discworld Companion).
Bel-Shamhoroth could definitely be seen as a version of H P Lovecraft's Cthulhu.
In Pyramids it seems he is still remembered and referred to by the people of the Djel as the Eater of Souls.
See also: Numerology, Wizard's magic