Some good history of Cocoa from Aaron Hillegass’s book Cocoa Programming.
The window server on Mac OS X is like the X window server on Unix. It gets events from the user, forwards them to the application, and puts data on the screen.
NeXTSTEP came up with a set of libraries to enable programmers to deal with the window manager in an elegant manner. These frameworks were originally called OpenStep, which was later renamed Cocoa.
Programmers loved OpenStep. Tim Berners-Lee developed the first Web browser and the first Web server on NeXTSTEP.
Apple selected NeXTSTEP as there next operating and bought the whole company in December 1996.
NeXTSTEP became Mac OS X. It’s Unix underneath.
Cocao Touch is built on top Cocoa (many of the classes are identical). Most importantly, the principles and design patterns are essentially unchanged.