Ray Dolby died yesterday of Leukemia.
He is the reason audio tapes (at least those recorded with Dolby B and played back on Dolby B devices, which was most cassette tape players by the mid 80s, even portable cassette players had dolby built-in) didn't hiss in the high frequencies.
Dolby's company continued to make improvements to audio, particularly in the theater business, and Dolby Digital surround sound is the most common surround sound in the theaters today. If you recall, old movies seemed to have very loud high frequencies, sometimes to the point where clipping occurred. This was due to the inevitable hiss that would end up in the final print due to the optical audio technology. Dolby film sound and later Dolby Stereo and Dolby Surround sound eliminated this problem - the first film to use Dolby was A Clockwork Orange, and now every movie uses the same technology (though, of course, patents expire and most sound is now digital).
AAC, most commonly used by Apple and direct competitor to mp3, was developed by Dolby.