Although they weren't the first to put big tires, flat handlebars, cantilever brakes, or even derailleurs, on a bike built for the mountains, they did spawn all of mountain biking as we know it today. From a few of these pioneers came the marketing, innovations and technologies that tipped mountain biking into the mainstream.
To most, names like Joe Breeze, Otis Guy, Gary Fisher, and Tom Ritchey don't mean much, but those of us who know the industry, these guys are the ones who built it. Mike Sinyard who joined in just a little later should also get quite a bit of credit for bringing the first real mass produced mountain bikes to the market.
From there, it's just been one innovation after another for nearly 30 years.