This picture shows the timeline of unix development since the early days of Unix-PDP7 from 1969 to 2007. A good referance for history bums. Taken from Wikipedia and converted in to png (orginal picture was in .svg format)

From wikipedia:

In the 1960s, the Massachusetts Institute of Technology, AT&T Bell Labs, and General Electric worked on an experimental operating system called Multics (Multiplexed Information and Computing Service), which was designed to run on the GE-645 mainframe computer. The aim was the creation of a commercial product, although this was never a great success. Multics was an interactive operating system with many novel capabilities, including enhanced security. The project did develop production releases, but initially these releases performed poorly.

AT&T Bell Labs pulled out and deployed its resources elsewhere. One of the developers on the Bell Labs team, Ken Thompson, continued to develop for the GE-645 mainframe, and wrote a game for that computer called Space Travel. However, he found that the game was too slow on the GE machine and was expensive, costing $75 per execution in scarce computing time.

Thompson thus re-wrote the game in assembly language for Digital Equipment Corporation’s PDP-7 with help from Dennis Ritchie. This experience, combined with his work on the Multics project, led Thompson to start a new operating system for the PDP-7. Thompson and Ritchie led a team of developers, including Rudd Canaday, at Bell Labs developing a file system as well as the new multi-tasking operating system itself. They included a command line interpreter and some small utility programs.

For an in-depth history lesson check out this wikipedia entry: http://en.wikipedia.org/wiki/Unix

Get more history lessons on Unix from these sites:
http://www.levenez.com/unix/
http://www.bell-labs.com/history/unix/
http://www.unix.org/what_is_unix/history_timeline.html
http://cm.bell-labs.com/cm/cs/who/dmr/hist.html
http://www.ussg.iu.edu/usail/concepts/unixhx.html
http://www.hsrl.rutgers.edu/ug/unix_history.html
http://www.dei.isep.ipp.pt/~acc/docs/unix-Part_I.html
http://www.faqs.org/docs/artu/ch02s01.html
http://www.computerhope.com/history/unix.htm
http://www.crackmonkey.org/unix.html
http://www.dwheeler.com/secure-programs/Secure-Programs-HOWTO/history.html
http://www.uwsg.indiana.edu/usail/external/recommended/unixhx.html