Gygax was responsible for creating or adapting the game's spells, races, and character classes (cleric, fighter, etc.). Perhaps his essential contribution was to develop a way to translate physical characteristics into numbers. An American Gladiator, for example, might have a "strength" of 18, while a Woody Allen-like character might have a four. In combining math and fantasy, Gygax engineered a cocktail that no geek could resist. It was also his idea to create "levels" and "experience points," allowing a character to become more skilled as you spend more time with the game. This idea made the game impossibly addictive and helped yield $1 billion in worldwide sales (according to the BBC), scores of books, miniature sets, board games, a cartoon show, and a pretty crummy movie.
D&D fans were often super fans. Many painted their own figurines, went to conventions dressed up as orcs, or spent nights and weekends gaming. As opposed to other geeky addictions, though, this one was social (kind of). While it might have been socially detrimental to be known as the best dungeon master in all of middle school, it's also true that some people just don't fit in very well. D&D can provide a social outlet and a way to kick ass without being afraid of getting your ass kicked. Running a D&D campaign took a lot of paperwork, a lot of organization, and a lot of focus. I spent hours creating creatures, towns, and dungeons that that I didn't always end up using. I liked some of these scenarios so much I turned them into stories, and these experiences were one reason I decided to become a writer.
While Dungeons & Dragons has been a source of inspiration for innumerable people in the last three decades, none of Gygax's post-D&D projects proved particularly successful. Quarrels with staff led to his departure from his company, Tactical Studies Rules, in 1985. Both he and TSR failed to take the lead in the newest role-playing sensations, most notably video games (some of the D&D games did well, but Gygax's online RPG Lejendary Adventure Online never got off the ground) and collectible card games (TSR was eventually bought by Wizards of the Coast, owner of the mega-successful Magic: The Gathering franchise).
Some people have blamed Gygax's failings on the fact that he was always more gamer than businessman. He grew unhappy with later versions of D&D, declaring them "rule intensive" and more focused on singular achievements than group cooperation. Perhaps his purist belief in an anything-goes fantasy world became out of fashion in the greedy 1980s and disaffected 1990s. For whatever reason, people grew more interested in turning their characters into godlike beings and got less focused on the intricacies of team play. (Sort of like the NBA.)
Despite his late-career failings, Gygax's innovations have continued to spread. In creating the greatest nerd hobby of all time, he built the foundation of every future role-playing game. His idea to assign numbers for health, armor, stamina, and magic has also provided the backbone for innumerable video games, including the Final Fantasy series and the blockbuster World of Warcraft. Wherever geeks cluster, whether playing a Pokemon card game or a video game like Oblivion, they're playing by the rules that Gary Gygax laid out. It's fitting that through Gygax's creativity and inspired descendents, the realm of nerddom has found eternal life.