He was a "big deal" in the 90s, at least within hacker circles: wrote a lot of early free software / hacker culture reated stuff & was heavily involved in the rebranding of "free software" into a form that corporate suits could feel comfortable with ("open source") & selling that idea to a wider audience. See 'The Cathedral & the Bazaar' and other works.

He wasn't all talk: way back in the day, he worked on emacs & authored fetchmail (fair warning: reading the fetchmail source will make your ears bleed.)

More on his wikipedia page: http://en.wikipedia.org/wiki/Eric_S._Raymond