Dennis Ritchie has a place in history that few men have ever achieved, because his work helped change the world. I am a young man compared to the late DMR but I does have an interest in history. If it wasn't for this mans work, I doubt that I could be writing this journal entry, because he helped to enable so many elements that make it possible.
His most famous programming language, C, was so pervasively popular, that I knew of it before I learned to program. My first programming language (C++) was derived from it. A big part of how I fell so deep insane with computers was learning about how C and Unix became self hosting. That means you could make C and Unix using C and Unix, in laymans terms. Back then that was almost like revolutionary - today it's like sliced bread. We take it for granted but someone had to help show us the way; then people started to use it everywhere.
Through C, we gained countless programs. Most Unix operating systems are written in C, most other operating systems are written in C or finally grown from one that was. Unix, DOS, Windows, Linux, OSX, your iPod, your iPhone, your iPad, our Android. None of it would exist just like it does. Most of the stuff we do every day involves C programs, be that reading e-mail, playing games, surfing the web. It is even normal for other programming languages to be implemented in C. The defacto standard Perl, Python, and Ruby included. It is so normal that writing a language implementation in itself is not so big anymore. C is so pervasive that it is also inescapable in other languages: their is almost always a way and a need to interface with C code. Hell, today you might even have C code involved in your toaster. It is that important a programming language. If you ever used a computer or an embedded system, you have probably used software written in C, or are old enough to remember what it was like before punch cards.
C is perhaps the single most important language since programmer's stopped writing in raw machine code. In fact, sometime after that we stopped writing in assembly and I know no one who goes lower level than reading the machine code. A common portion of C syntax is practically our linga franca—even if C is not a shared language, the syntax (which grew from prior languages) is also widely used and an alternative to pure pseudo code.
Maybe a lot of young programmers don't know C, or skip it. I love it. It is one of the most beautiful languages that I know, despite it's trappings. Perhaps some of the greatest lessons I learned about my craft, was that learned from C. Perhaps another was the humility of it's creator.
Somehow, I doubt his other works will ever be as well known as C, or things he was a big part of (like Unix), but maybe people will study them and see what they can learn from the work of a legendary hacker, like Dennis Ritchie.