Stephen King said, after endless questions from his fans, Randall Flagg was heavily inspired by Narly, but he wasn't him himself
I like the interpretation of Slenderman being him though. Acts like him too (fucking with his preys mind, driving them to near madness, before going in and bringing them to a fate worse then death)
But yeah, besides the Big C, Narly is easily Lovecrat's most iconic character, and he's the one people seem to take so much inspiration from.