Serpentfolk

Serpentfolk are a somewhat obscure idea that seems to base itself on the idea "lizardfolk are kind of cool, but how can we make them cooler and/or more evil? Hmm... let's base 'em on snakes!" and working from them.

Serpentfolk, known at the time as Serpentmen or Snakemen, first appeared in the works of Robert E. Howard as part of his King Kull stories, more obscure "predecessors" to those of Conan the Barbarian. Serpentfolk were depicted as a pre-human sapient species of black magicians that had dominated the world, until Atlantis had arisen and defeated them. They also were slowly and tentatively assimilated into first the Conan stories and then, through Howard's correspondence with H.P. Lovecraft, into the Cthulhu Mythos. This is something cemented by the fact that Lovecraft (alongside Zealia Bishop) created a paron deity for the Serpentfolk in the form of Yig, Father of Serpents, in the story "The Curse of Yig".

As such, Cthulhan Serpentfolk have repeatedly appeared in the various editions of Call of Cthulhu.

Over in Dungeons & Dragons, although serpentfolk haven't directly appeared, the Yuan-Ti, a species of human/snake hybrids who are divided into castes based on how great the ratio of human to snake is, with the more serpentine being more respected, and with a propensity towards all kinds of fucked up mutations, are pretty obviously made in the Serpentfolk mold. They play a big role in the backstory of the Forgotten Realms.

Pathfinder, meanwhile, being unable to use Yuan-Ti, simply said "fuck it" and paid the Lovecraft estate for the right to use Serpentfolk outright.