Greyhawk
Greyhawk, also known as the World of Greyhawk, is a fictional world designed as a campaign setting for the Dungeons & Dragons fantasy roleplaying game. Although not the first campaign world developed for Dungeons & Dragons—Dave Arneson's Blackmoor campaign predates it by a few months—the world of Greyhawk was the setting most closely identified with the development of the game from 1972 until 2008. The world itself started as a simple dungeon under a castle designed by Gary Gygax for the amusement of his children and friends, but it rapidly expanded to include not only a complex multi-layered dungeon environment, but also the nearby city of Greyhawk, and eventually an entire world. In addition to the campaign world, which was published in several editions over twenty years, Greyhawk was also used as the setting for many adventures published in support of the game, as well as for RPGA's massively shared Living Greyhawk campaign from 2000–2008.
Early development
In the late 1960s, Gary Gygax, a military history buff and pulp fantasy fan, started to add elements of fantasy into traditional tabletop medieval miniatures wargames at his games club in Lake Geneva, Wisconsin. He sometimes replaced typical medieval weapons with magical spells, or used dragons and other fantastical monsters in place of soldiers. In 1971, as part of a rule set for tabletop battles called Chainmail that he was co-writing, he created supplementary rules for magical spells and monsters as well as one-on-one combat.