Greg Stafford began wargaming after picking up a copy of U-Boat by Avalon Hill, and in 1966 as a freshman at Beloit College he started writing about the fantasy world of Glorantha. After rejection from a publisher, Stafford created White Bear and Red Moon set in Glorantha, and after three different companies were unable to publish the game he created Chaosium. He derived the name partly from his home, which was near the Oakland Coliseum, and combining "coliseum" with "chaos." White Bear and Red Moon (1975) was Chaosium's first published game. White Bear and Red Moon was also Stafford's first professional game. Stafford designed the board game Nomad Gods. Stafford also designed the wargames Elric (1977) and King Arthur's Knights (1978).
Stafford wanted the world of Glorantha to be part of an original role-playing game; this ultimately resulted in Steve Perrin's RuneQuest (1978), which was set in Glorantha. Stafford and Lynn Willis simplified the RuneQuest rules into the 16-page Basic Role-Playing (1980). He designed the miniatures game Merlin. Stafford considers his 1985 role-playing game King Arthur Pendragon his masterpiece. He co-designed the Ghostbusters role-playing game. Stafford designed the Prince Valiant roleplaying game, published in 1989, which featured a strong storytelling basis and other innovations. Stafford decided to produce a fiction line for Call of Cthulhu after he realized that many Lovecraft fans of the early 1990s had never actually read Lovecraft's fiction but were only familiar with him through Call of Cthulhu.
Stafford left Chaosium in 1998, taking all of the rights for Glorantha, and founded the game company Issaries. Stafford co-designed the computer game King of Dragon Pass. Stafford approached Robin Laws to create a new game based on Glorantha, which became known as Hero Wars, published in 2000 as the first fully professional product for Issaries. Stafford published the second edition in 2003 under the name he always wanted HeroQuest, as Milton Bradley's trademark on the name had lapsed. Stafford moved to Mexico in 2004, bringing production from Issaries to an end. When Hasbro let the RuneQuest trademark lapse, Stafford picked up the rights to the game and licensed Mongoose Publishing to publish a new edition in 2006. After White Wolf acquired the rights to Pendragon, their ArtHaus imprint published The Great Pendragon Campaign (2006), in which Stafford detailed the massive RPG campaign from the years 485 to 566. After Nocturnal Games picked up the rights to Pendragon, Stafford created a 5.1 edition of Pendragon (2010).
Stafford is perhaps most famous as the creator of the fantasy world of Glorantha, but he is also a prolific games designer. He was designer of Pendragon, he was co-designer of the RuneQuest, Ghostbusters, Prince Valiant and HeroQuest role-playing systems, founder of the role-playing game companies Chaosium and Issaries, designer of the White Bear and Red Moon, Nomad Gods, King Arthur’s Knights and Elric board games, and co-designer of the King of Dragon Pass computer game.
Greg Stafford's interest in roleplaying and gaming originated in his adolescent fascination with mythology. During his adolescent years he read anything he could find on the subject, and when he exhausted the libraries, he started to write his own stories in his freshman year at Beloit College, in 1966. This was the start of the world of Glorantha.
Stafford's 1974 board game White Bear and Red Moon had featured the violent struggle between several cultures in the Dragon Pass region of Glorantha. The heart of the game was a conflict between the barbarian Kingdom of Sartar and the invading Lunar Empire, a theme which has remained central to Gloranthan publications since then.
As Stafford was founding his company Chaosium, the game Dungeons & Dragons (and the concept of tabletop role-playing games) was gaining great popularity. Role-players were keen to use the White Bear and Red Moon setting in such games. So Chaosium published RuneQuest, written by "Steve Perrin, Ray Turney, and Friends". Stafford left Chaosium in 1998. He moved from Berkeley, California to Arcata, California in 2007, having lived in the San Francisco Bay Area for some years.
Glorantha has been the focus of his life's work, but Greg considers his masterpiece to be the Arthurian chivalric role-playing game Pendragon, published in 1985 by Chaosium, republished in 2005 by White Wolf. Stafford won the Diana Jones Award, 2007, for his work on Pendragon.
In 1999 Pyramid magazine named Greg Stafford one of The Millennium's Most Influential Persons, "at least in the realm of adventure gaming."
In June 2015, it was announced that Greg and Sandy Petersen had returned to Chaosium Inc., Stafford taking the positions of President and CEO.
Stafford is also a practicing shaman and member of the board of directors of Shaman's Drum, a journal of experiential shamanism. He has had some short articles of Arthurian interest published. Stafford recently lived in Mexico for 18 months, tutoring English as a foreign language, exploring places of archeological and shamanic interest.
For some years, Stafford has been slowly writing several novels set in Glorantha. Novels that he is known to have been working on are Harmast's Saga, Arkat's Saga, and his "Lunar novel".
He was one of the designers on the Glorantha-based video game "King of Dragon Pass".
Fantasy author David A. Hargrave pays homage to Stafford in the Arduin series of supplements, the most widely know example of this being the Stafford's Star Bridge 9th-Level mage spell (Arduin I, page 41).
He was honored as a "famous game designer" by being featured as the king of hearts in Flying Buffalo's 2011 Famous Game Designers Playing Card Deck.