Unix is an operating developed at Bell Labs primarily by Dennis Ritchie and Ken Thompson .
It is basically the building blocks for all modern operating systems and it’s derivates run on most of the machines that power the internet.
You can read more about Unix in Lions Commentary on Unix .
“You often have this well told story of Ken Thompson finding a little used PDP-7 upon which he builds, in a month, an operating system. And the rest is Unix history” - Brian Kernighan