Greyhawk is the first supplementary rulebook for the original edition of the Dungeons & Dragons fantasy role-playing game and written by Gary Gygax and Robert J. Kuntz. It addeda combat system, making D&D a truly stand-alone game system separate from Chainmail.
Greyhawk introduced new character classes thief and paladin, new combat rules, spells, monsters, and treasures. It included new rules on weapon damage varying by weapon, new treasure and magic items, and new spells, including 7th, 8th, and 9th level spells. The supplement also included a section on monsters, introducing the lizard men, beholders, displacer beasts, blink dogs, carrion crawlers, and many others.