As I mentioned, my current M&M:W&W (how's that for an abbreviation!) is a an attempt to create a "D&D world" outside of the D&D ruleset. It's largely a continuation of my last GURPS game which utilized the then-brand-new Dungeon Fantasy line.
In getting ready for that game, I did what one should always do when trying to emulate another work. I took a look at said work's inspirations. This led me to revisit Gygax's Appendix N from the Dungeon Master's Guide. I focused particularly on what he called "the most immediate influences on AD&D."
The list is heavy on pulp authors. I've read that the pulp revival of the late sixties-seventies was due to a publishing hunger for fantasy in the wake of the sixties popularity of Tolkien. Given Gygax's age, he almost certainly had an earlier exposure to these authors than that. He may have began reading the Gnome Press editions of Conan from the fifties. Maybe he discovered Frtiz Leiber's Fafhrd and Gray Mouser in the 1957 collection, The Two Sought Adventure, or perhaps he read some of the stories from the pages of the pulps themselves. The De Camp/Pratt "Incomplete Enchanter" stories extant at the time had first appear in the pulps in the forties, but had begun appearing in collections or novel expansions that were likely still around soon thereafter. Vance's The Dying Earth had first been published in 1950. Wherever he encountered them, Gary Gygax was widely read in the fantasy genre as it existed at that time.
Let's just look at the biggest influences and see what they have in common: Leiber and Howard are "sword and sorcery" with protagonists out for personal, material gain--certainly not out to save the world. De Camp and Pratt, Vance, and Leiber, often have a humorous, ironic tone (perhaps owing a debt to James Branch Cabell who unfortunately doesn't make the list). De Camp and Pratt's Incomplete Enchanter series has a mechanistic, rational approach to the irrational (magic). Merritt gives us "lost worlds" with characters encountering exotic, hidden locales (like a lot of gaming modules). Lovecraft has outre monsters, and subterranean weirdness (as does Leiber in at least a couple of stories). Vance's and Leiber's tales are often picaresque.
So here's what, it seems to me, made it into D&D:
1. Interest more in material gain (treasure) and personal advancement (becoming a person of quality/leader of men--but perhaps not succeeding). This is in contrast to the more "epic hero" goals found in Tolkien and most modern series fantasy.
2. Gritty, lower powered heroes, rather than empowered demigods/epic heroes.
3. Weird/fantastic locales (often ruins of another age or subterranean realms) where dangers may be encountered and treasures gained.
4. (from Vance and some De Camp/Pratt) well defined "rules" of how magic works making it rather mechanistic, and putting magic into the hands of "heroes" not just depraved antagonist "sorcerers" or enigmatic wizardly advisers.
A good starting point for a game of fantasy adventure. Sources to conjure with.
But Gary and crew didn't stop there. Over the evolution of this phenomena called D&D, the game became a thing unto itself with its own tropes and characteristics not found in the source material--or at least differently emphasized. Without these innovations, D&D wouldn't be D&D, as it's commonly conceived.
Next time, I'll try to identify what I think these might be.
42 minutes ago