Gary Gygax was the principle creator of the game "Dungeons & Dragons" waaaaay back in the 1970s. I've played D&D all of about half a dozen times, but I always found the Monster Manuals and whatnot to be pretty interesting, and there's no denying the role of D&D in the Satanic Panic of the 1980s. Entire books, none of them convincing, have been devoted to how D&D threatens to annihilate the entirety of western civilization, while the more grounded among us still acknowledge that the influence of D&D on popular culture is almost incalculable. Gary Gygax clearly had more of an impact on society than he ever could have imagined when he first started to write up a game about elves fighting unicorns.
In any event, he has passed away at the age of 69. Nerds everywhere (myself included) have lost a kindred spirit.
The guys over at Penny Arcade have drawn up a tribute more fitting than anything I could come up with here. Enjoy.