Cthugha, Shub‑Niggurath, Nyarlathotep, Azathoth, Yog‑Sothoth
Exploring the Cthulhu Mythos: Nodens
Nodens (Lord of the Great Abyss or Nuada of the Silver Hand) is a fictional character in the Cthulhu Mythos. Based on the Celtic deity, Nodens, he is the creation of H. P. Lovecraft and first appeared in his short story "The Strange High House in the Mist" (1926).
And upon dolphins' backs was balanced a vast crenelate shell wherein rode the grey and awful form of primal Nodens, Lord of the Great Abyss… Then hoary Nodens reached forth a wizened hand and helped Olney and his host into the vast shell.—H. P. Lovecraft, "The Strange High House in the Mist"
Nodens is one of the Elder Gods and appears as an elderly, human male with white hair—gray-bearded and hoary yet still vital and strong. He often rides in a chariot formed from a huge seashell pulled by some great beasts of legend. Nodens is served by the Nightgaunts.
As a hunter, he will chase down evil creatures in the Dreamlands, such as the Shantaks. He prefers to hunt the servants of the Great Old Ones or Nyarlathotep because they are usually the most intelligent and offer the best sport, but not necessarily because he wants to help humans being attacked by them. He has, however, been known to deliberately help humans, such as when he offers advice to assist Randolph Carter against Nyarlathotep in The Dream Quest of Unknown Kadath: "Out of the void S'ngac the violet gas had pointed the way, and archaic Nodens was bellowing his guidance from unhinted deeps," later followed by "And hoary Nodens raised a howl of triumph when Nyarlathotep, close on his quarry, stopped baffled by a glare that seared his formless hunting-horrors to grey dust."
Lovecraft may have based Nodens on Arthur Machen's The Great God Pan (1890) because Machen was one of Lovecraft's favorite authors. In the novel, Machen describes a late Roman inscription hinting that Nodens is actually the titular god Pan.
On one side of the pillar was an inscription, of which I took a note. Some of the letters had been defaced, but I do not think there can be any doubt as to those which I supply. The inscription reads as follows:DEVOMNODENTiFLAvIVSSENILSPOSSVitPROPTERNVPtiasquaSVIDITSVBVMBra
'To the great god Nodens (the god of the Great Deep or Abyss) Flavius Senilis has erected this pillar on account of the marriage which he saw beneath the shade.'—Arthur Machen, The Great God Pan
Machen was probably inspired by the finding of an extensive temple complex dedicated to Nodens at Lydney Park in Gloucestershire.