Gary Gygax, co-creator of the first role-playing game Dungeons and Dragons, has died at the age of 69.
The game Gygax co-created became part of youth sub-culture
Gygax, who developed the game in 1974 with Dave Arneson, had been suffering from health problems for several years.
Famous for its mythical creatures and odd-shaped dice, Dungeons and Dragons was an instant success that spawned a slew of video games, books and films.
Gygax was also an author who wrote numerous fantasy books, including the Greyhawk series of adventure novels.
He died on Tuesday at his home in Lake Geneva, Wisconsin, leaving a wife and six children.
Ernest Gary Gygax grew up in Chicago, moving to Lake Geneva at the age of eight.
His father, a Swiss immigrant, read fantasy books that got his son hooked on the genre, according to Gygax's widow Gail.
Gygax was working as an insurance underwriter in the 1960s when he began playing war-themed board games.
It was these that inspired him and Arneson to develop Dungeons and Dragons, in which players create fictional characters by rolling dice that determine their skills and abilities.
An estimated 20 million people worldwide have played the game, with more than $1bn (£505m) spent on equipment and books.
"I thought we would sell about 50,000 copies," Gygax told the BBC News website in 2004.
D&D rules grew out of war gaming in the early 1970s
Gygax and Arneson sold their rights to Dungeons and Dragons in the 1990s, when the game's popularity began to wane.
According to his widow, though, he hosted weekly games as recently as January.
"It really meant a lot to him to hear from people from over the years about how he helped them become a doctor, a lawyer, a policeman," she said.