Dennis Ritchie may not be as great a household name as Jobs and Gates, but he did something neither of them ever achieved: he wrote code that worked. As the developer of the C programming language, he enabled the work of every programmer whose work depended on it -- developers who worked on OpenBSD, Mathematica, Apache, Linux ... and Microsoft Office, Microsoft Windows, Microsoft Internet Information Server (IIS, which has apparently had its unabbreviated name changed to end with the word "Services"), Microsoft Bob ... you name it. Even MacOS X and everything written using the Cocoa API. There are some folks who wrote programs in Cobol or Fortran, to be sure – but if you're like most of the people on the planet you've not only never run such a programs but never owned a machine that did.
Dennis Ritchie's operating system work further illuminated his philosophy: lots of specialist tools, ready to work in concert to perform complex tasks ... none of which needed to be able to do "everything" to get its job done, all of which were consequently lighter on resources than tools that "had to do everything all by themselves." The simplicity of his systems made them strong; but like a game of go, their simplicity was easily lost on untrained observers. Indeed, Dennis Ritchie famously – and widely quoted in doing so – said "Unix is simple. It just takes a genius to understand its simplicity."
Dennis Ritchie, benefactor of mankind, has departed to prepare the Great Product In The Sky (which, being the rockingest product of its kind, Jobs will surely be set to demo).