Ted Ts'o
The Linux developer who wrote /dev/random and led Kerberos work at MIT — two of the most widely used security building blocks in the Unix world.
Theodore Ts'o was one of the first Linux developers outside Finland and ran the early tsx-11 FTP mirror at MIT. In 1994 he wrote the kernel's random number generator, which gathers noise from interrupts and keystrokes into an entropy pool and hands it out through /dev/random and /dev/urandom. Nearly every Unix variant copied the idea.
In parallel he was technical lead for Kerberos version 5 at MIT and active in the IETF's IPsec work. Outside security he's best known as maintainer of e2fsprogs and the ext4 file system. He has also been an outspoken critic of blindly trusting the CPU's own random-number instruction — a position that looked a lot less paranoid after Snowden.