Dungeons & Dragons co-creator Dave Arneson, whose fantasy role-playing game guided the socially awkward through adolescence, has rolled his last dice. Arneson, the Associated Press reports, died on Tuesday of cancer in St. Paul, Minn., at the age of 61. He and Gary Gary Gygax – who died last March -- invented D&D in 1974, and the game became a cult favorite among geeky teen boys, giving way, as ScientificAmerican.com tech editor Larry Greenemeier notes, to the nerd power of the 1980s embodied by Bill Gates. (It is also a favorite of a number of actors, including Vin Diesel, who...