Steve Bellovin
One of the three grad students behind Usenet in 1979, who later co-wrote the book that made the firewall a household concept among sysadmins.
At the University of North Carolina, Bellovin wrote the very first news software — a handful of shell scripts — while Tom Truscott and Jim Ellis at Duke supplied the idea of shipping discussions between machines over UUCP. The scripts were soon replaced by A News in C, but the basic shape of groups and site-to-site forwarding was already there.
At AT&T Bell Labs he and Bill Cheswick published Firewalls and Internet Security: Repelling the Wily Hacker in 1994, which made the firewall the default answer to the question of how to protect a network. He later became a professor at Columbia University. Few people were there both when the net was built open and when it had to be closed again.