From Knoppix Documentation Wiki
The UNIX® system is a portable computer operating system originally developed by a group of AT&T Bell Labs employees including Ken Thompson, Dennis Ritchie and Douglas Mc Ilroy.
In 1983, Richard Stallman announced Project GNU, an ambitious effort to create a freely redistributable UNIX-like system. The software developed in this project -- such as GNU Emacs and gcc -- has gone on to play central roles in other free UNIX systems as well.
When in 1991 Linus Torvalds began to put forth the Linux kernel and gather contributors, the GNU tools were an obvious match. When combined with the Linux kernel, the GNU software formed the foundation for a POSIX-conformant operating system known as GNU/Linux -- or just Linux. Distributions of the kernel, GNU, and additional software -- such as Red Hat Linux and Debian GNU/Linux -- have become popular both with hobbyists and in business