Sam Leffler has been actively working with Unix systems since 1976 when he first encountered a PDP-11 at Case Western Reserve University, and he has been involved with what people now think of as open source long before it was even termed "open source". While working for the Computer Systems Research Group at the University of California at Berkeley he helped with the 4.1BSD release and was responsible for the release of 4.2BSD. He has contributed to almost every aspect of BSD systems, most recently working (again) on the network subsystem.
After his time at Berkeley he spent time at Lucasfilm, Pixar, Silicon Graphics, and VMware before striking out on his own as an independent consultant. His most recent work is focused on wireless networking for use in the open source community.