You could call him the Wozniak to Gary Gygax's Steve Jobs, but while Dave Arneson never appeared on the Simpsons, there would be no RPG industry today without his vision of a fantasy "campaign" as more than wargaming with druids. So let us raise a toast in thanks to the man who put dungeons in Dungeons and Dragons.
PS: I should mention also that Keith Herber of Call of Cthulhu fame passed away back on March 13th as well. It's not a happy time for old-school gamers. :(