Short answers, pulled from the story.
Appendix N is a list of inspirational and educational reading found in Gary Gygax's 1979 Dungeon Master's Guide. It specifies twenty-eight authors and twenty-two specific books that formed the core source material for early game mechanics.
The original list includes names like Leigh Brackett, Fredric Brown, H.P. Lovecraft, Robert E. Howard, Fritz Leiber, and Clark Ashton Smith. It also features series such as Edgar Rice Burroughs' Pellucidar and Barsoom collections.
Dungeons and Dragons adopted a memorized spell system known as Vancian magic after Jack Vance's work. Vance freely gave permission to use his Ioun Stones as magical items on the condition that his books received mention.
TSR faced papers threatening damages totaling half a million dollars from Elan Merchandising acting on behalf of the Tolkien Estate. They were ordered to remove Balrog, Dragon, Dwarf, Elf, Ent, Goblin, Hobbit, Orc, and Warg from the game due to copyright disputes.
Joseph Goodman read every book in Appendix N to create the Gygax-inspired OSR RPG Dungeon Crawl Classics. Many published modules for that game directly reference texts such as Peril on the Purple Planet inspired by Edgar Rice Burroughs.