Dennis Ritchie and Ken Thompson at a pretty well maxed out DEC PDP11 computer and two Teletype model 33 terminals.
See Unix's timeline at: en.wikipedia.org/wiki/Unix
See Unix's story at Bell Labs: www.bell-labs.com/history/unix/
See Unix's evolution at: cm.bell-labs.com/cm/cs/who/dmr/hist.html
For those interested in telephone related uses of Unix see below: