Dungeons & Dragons creatures from folklore and mythology

Creatures from the Dungeons & Dragons fantasy role-playing game that come from or are based on real-life folklore or mythology. Note that many of these, although taking the name from the mythological version, have very little in common with them, instead being based on modern fantasy fiction. Elves and Dwarves in D&D, for example, are based more upon those of J.R.R Tolkien than anything else.