Gary Gygax, who died yesterday at 69, was the ultimate dungeon master.

Together with a friend, Dave Arneson, Gygax developed the groundbreaking role-playing game Dungeons & Dragons, which spread to high schools and college campuses across the nation starting in 1974.

RPGs, as their enthusiasts call them, were initially isolated in communities of socially awkward young men listening to heavy-metal music and pretending to be goblins. Today they have grown to include millions of socially awkward people, of all ages and sexes and musical tastes, connected by the Internet and pretending to be everything from goblins to glamorous models.

It was “an entirely new type of hobby that now attracts millions of players worldwide to face-to-face and online role-playing games,” according to a statement issued by D&D’s publisher, Hasbro Inc.’s Wizards of the Coast unit.

Born July 27, 1938, in Chicago, Gygax grew up reading science fiction and fantasy works by Ray Bradbury, L. Sprague de Camp, and H.P. Lovecraft. After dropping out of the University of Minnesota, he became an insurance underwriter. In his spare time, he helped found the International Federation of Wargamers, a group of enthusiasts scattered around the Midwest. Eventually, Gygax and his cronies began creating dark-ages-themed games in which the participants took on the actual roles, rather than moving groups of tokens around a board.

Dungeons & Dragons was the result of Gygax and Mr. Arneson’s attempts to systematize their games. The game was heavily influenced by J.R.R. Tolkien, and many of the monsters that inhabit D&D — balrogs, orcs, ringwraiths — were lifted wholesale from Tolkien’s Middle Earth.

“We even used the term Hobbit at first,” Gygax told the Knight Ridder news service in 2001. But Tolkien had copyrighted the term, so Hobbits became “Halflings.” Among the game’s signature items was a die with 20 sides.

Marketed mainly by word of mouth, D&D sold its first thousand units in less than a year and then jumped dramatically. In 1977, a more complex version of the game was released with a thick rule book. Gygax got used to getting midnight calls from players wondering about some technicality or other.

“Much of that detail went in there because the players wanted it,” Gygax told Forbes in 1980. He was particularly proud of the “Dungeon Master’s Guide’s” chart of herbs and spices that allowed players to create their own potions.

The game became the focus of controversy in 1979 when a Michigan State University student went missing in steam tunnels below the school’s campus and was rumored to have been playing D&D. Role-playing games were denounced by Christian groups, and a “60 Minutes” report seemed to link D&D to a pair of suicides. Gygax received threats and hired a bodyguard, but the publicity only increased sales. He also oversaw production of a short-lived D&D cartoon series.

After breaking in the 1980s with Tactical Studies Rules Inc., the company he helped found to market Dungeons & Dragons, Gygax went on to create several other role-playing games, including Dangerous Journeys and Lejendary Adventures, as well as a form of three-dimensional chess. He wrote more than a dozen novels featuring a cast of characters similar to those in D&D, starring the ominously named “Gord the Rogue.” He also published books about how to create fantasy games.

Gygax enjoyed hearing from the game’s legion of devoted fans, many of whom would stop by his family’s home in Lake Geneva, Wis. Despite his declining health, he hosted weekly games of Dungeons & Dragons as recently as January, his wife told the Associated Press. She and their six children survive him.

Among the accolades his career garnered was Arthronema gygaxiana a species of bacteria named for him. He placed first on Sync Magazine’s list of “The 50 Biggest Nerds of All Time.”