As stated in his Wikipedia entry, Gernsback not only founded the first science fiction magazine, Amazing Stories, but he also founded an early radio station, was an avid amatuer radio pioneer, and was involved in the first broadcasts of television. He also founded Modern Electronics, the first magazine devoted to electronics. At the time of his death he held over 80 patents.
His specific contributions to the science fiction genre start even with the name as detailed on the Hugo Gernsback's Forecast website. No less of a figure than Isaac Asimov continued to use Gernsback's original term "scientifiction" for the genre to his deathbed. Hugo Gernsback was one of the very first inductees to the Science Fiction and Fantasy Hall of Fame in 1966, and of course the Hugo award for excellence in SF writing bears his name as well. It says something about what a big figure he really was to the genre that it was his first name which was chosen for the name of this award!
While it is rather obvious that Gernsback's publishing and editing accomplishments overshadow his writing, nonetheless, his best known book, the novel Ralph 124C 41+ can be read in it's entirety online courtesy of Google.







