Deities & Demigods (1980) was the fourth hardcover release for Advanced Dungeons & Dragons and the final book that Gary Gygax conceived of when he originally laid out the plans for the Advanced Dungeons & Dragons line in The Dragon #14 (May 1978).
The AD&D Line. Deities & Demigods followed the Monster Manual (1977), the Player's Handbook (1978), and the Dungeon Master's Guide (1979). Whereas Gygax called the previous three books "the main parts," he acknowledged that Deities was a "supplement." It was released around August 15, 1980, which means that many gamers would have seen it for the first time at GenCon XIII (August 21-24, 1980).
Despite being "just" a supplement, Gygax saw Deities & Demigods as integral to the AD&D line. This was because he thought that GMs were alternately either neglecting deities (by never mentioning them) or abusing them (by bringing them constantly on stage). He wanted to offer a middle-ground where deities could take their proper spot in D&D campaigns as the patrons of clerics and as the exemplars of alignment.
Sadly, despite Gygax's original intent, Deities & Demigods was very much a list of deities that could be killed - especially after the release a few months later of Q1: "Queen of the Demonweb Pit" (1980), in which the players (probably) killed the goddess Lolth. It wasn't until the second edition of AD&D that the focus on deities turned toward their religions rather than their stats.
A Second-Generation Book. Of all the AD&D hardcovers, Deities & Demigods was the only one that purposefully and directly revamped material from the Original Dungeons & Dragons (OD&D) game - more specifically from Supplement IV: Gods, Demi-Gods & Heroes (1976).
The original book was shorter and printed at digest size, so there was considerable room for expansion in the new one. This new space was largely taken up by new deities that hadn't appeared in the OD&D book, including American Indian, Arthurian, Cthulhu, Lankhmar, Nonhuman, and Sumerian pantheons. The Cthulhu Mythos was derived from Rob Kuntz's article "The Lovecraftian Mythos in Dungeons & Dragons" in The Dragon #12 (February 1978), while the Nonhuman Mythos was (mostly) a brand-new creation by Lawrence Schick and probably one of the most influential elements in the book for the future of the D&D game. Conversely, a Hyperborean pantheon that appeared in Gods, Demi-Gods & Heroes was removed from the new book, presumably due to a lack of rights.
The other thing that shrank in the new Deities & Demigods was the description of various magic items used by the deities. This was probably partly the result of the new AD&D game allowing for more consistent descriptions of items (with that sort of rule consistency being one of the main reasons that Gygax designed the new game) and partly the result of either the authors or editor Lawrence Schick doing a superb job of actually codifying and clarifying the items. Thus, in the OD&D book, Heimdall's sword, Hofud "slays Frost Giants with but a single hit" and "has the Vorpal blade ability as described in 'Greyhawk' but with the absence of the anti-magic circle." In Deities & Demigods the description simply says "This sword is a vorpal weapon, and is also a sword of frost giant slaying."
(That's also a pretty good description, in a nutshell, of why AD&D was considered a better game than OD&D.)
The Chaosium Connection. After publishing Deities & Demigods, TSR learned that another RPG publisher, Chaosium, held the gaming licenses for the Cthulhu Mythos and the Melnibonean Mythos that they'd included in the book. The two companies arranged a deal where TSR could continue using the two mythos and in exchange Chaosium got the rights to use the AD&D and D&D trademarks and game systems for their multi-system Thieves' World (1981) release.
Ironically, TSR dropped the Cthulhu and Melnibonean Mythos from the book in later editions anyway, decreasing it from 144 pages to 128. Various sources suggest that this was either because they didn't want to promote another game company's lines or because they were afraid that religious groups might find those mythos offensive.
Expanding the Outer Planes. Besides featuring deities, Deities & Demigods also provided one of the earlier looks at the "Great Wheel" cosmology used for D&D through 2008. The Great Wheel had been introduced by Gygax in The Dragon #8 (July 1977) and then had been brought into AD&D through the Player's Handbook. Deities & Demigods slightly expanded the descriptions of the planes and also introduced the para-elemental planes of dust, heat, ice, and vapor. Perhaps more importantly, it introduced Concordant Opposition - the neutral plane at the center of the Outer Planes that would be the heart of Planescape - and it was the first book to depict the Great Wheel as a wheel. Before than the Outer Planes had looked more like a Monopoly board, with the Astral Plane in the middle.
Future History. There was never another Deities & Demigods-style book for AD&D first edition from TSR, but new deities frequently appeared in Dragon magazine, the most famous being Roger Moore's "Point of View" articles that featured more nonhuman deities in Dragon #58-63 (1982) and Gary Gygax's "The Deities & Demigods of the World of Greyhawk" in Dragon #67-71 (1982-1983). Many heroes, some of them from fantasy books, appeared in the long-running "Giants in the Earth" column, from The Dragon #26 to Dragon #64 (1979-1982).
Around 1983, TSR updated the trade dress of their hardcover books. The new books had orange spines and an "Official Advanced Dungeons & Dragons" logo on the cover. When TSR reprinted Deities & Demigods with the new dress in 1985, they renamed it Legends & Lore. In Dragon #103 (November 1985), Gary Gygax said this was done "as a sop, or bowing to pressure from those who don't buy our products anyway" - which is to say fundamentalist religious groups, who had by then begun actively attacking TSR under names such as "B.A.D.D." (1982-?), or Bothered about Dungeons & Dragons.
About the Creators. Deities & Demigods was officially written "by James M. Ward with Robert J. Kuntz." This reflects the credits for Gods, Demi-Gods & Heroes, which was bylined "Kuntz & Ward." Kuntz had actually left TSR some years previous, in early 1977, because he wasn't getting to do sufficient creative work, so Ward did all of the writing for the new edition - as is reflected in the ranked credits. James Ward, meanwhile, started work in the Sales Department of TSR shortly after submitting Deities & Demigods to them. Though he wouldn't be writing D&D books in his day job, Gygax noted, "there are evenings and weekends to write new material and design modules." As it happens, Ward's RPG writing went largely on hiatus after he joined TSR, until various gamebooks got him back into writing around 1983.
About the Product Historian
This history of this product was researched and written by Shannon Appelcline, the author of Designers & Dragons - a history of the roleplaying industry told one company at a time. Please feel free to mail corrections, comments, and additions to firstname.lastname@example.org.