The setting of many of the RuneQuest editions (but not all), as well as the primary setting for HeroQuest. Glorantha was first discovered by Greg Stafford and is owned by Moon Design Publications. Jeff Richard is the Creative Director for the setting.
The background of Glorantha is split into three Ages (First, Second and Third). The Third Age is the primary setting for published material, although there was a Second Age setting book.
The Third Age
The Third Age is supported by the HeroQuest and RuneQuest (1st, 2nd, 3rd, & 6th editions) rules and supplements, as well as the setting of the Dragon Pass, White Bear & Red Moon, and Nomad God board games, and the King of Dragon Pass computer game. The Third Age witnesses the rise of the Lunar Empire of the Red Moon and culminates in the apocalyptic Hero Wars.
The Second Age
The Second Age was supported by the RuneQuest (MRQ) (sometimes known as the 4th edition) and RuneQuest II (5th edition), published by Mongoose Publishing. The Second Age is no longer supported by any current publications.
Players do use the rules system with the background they prefer (mix and match). (Also, some players use the Basic RolePlaying by Chaosium or OpenQuest instead).