The very first version of the UNIX operating system was born in Augustus 1969! Its early name was Multics (“Multiplexed Information and Computing Service“). Years after years new branches started to build a huge family of different operating systems, all of them descending from the same origin. It has always been my preferred environment and I used it since 1994! I worked with AIX, Linux, OpenBSD, SCO Unix, Solaris, Tru64 (Listed in alphabetical order to hide my preferences 😉 ). Happy Birthday UNIX!
Have a look at a good story of UNIX by Computer World.