Eric Steven Raymond (born December 4, 1957), often referred to as ESR, is a computer programmer and open source software advocate. He is the author of the Nethack Guidebook, and was a member of the core DevTeam for NetHack 3.1.0.
Raymond's name became known within the hacker culture when he became the maintainer of the "Jargon File". After the 1997 publication of important essay on programming "The Cathedral and the Bazaar", Raymond became, for a number of years, an informal representative of the open source movement.
Based on the extensive Wikipedia entry.