Since we're talking about origins of DnD media.. I have a recent one to share: The King of Elfland's Daughter.
Been listening to a lot of Loot the Body recently:
Which tickled a memory: hey, DCC has King of Elfland as a patron- didn't they have an adventure with that title? Nope, it's
the Queen of Elfland's Son.
I then go and look at Loot the Body's song description, oh hey
it's inspired by an original story from the early 1900's.
So of course DCC had an adventure inspired by it, they're
very Appendix N-minded folk. This is some ur-fantasy stuff we're looking at here. Obviously TKoED is inspired by earlier mythology, but a lot of stuff sprang out of authors reading TKoED.