I learned all the "usual" stuff about information theory etc. as it was presented in engineering and math and [non-computer] science classes several decades ago. By the time I got to it, everything associated with Nyquist (and, for worse, most of information theory) was pretty refined stuff that seemed like it went straight from common sense (e.g. sampling) to a bunch of hot air by hauty-tauty academics. Yeah, the sampling rule makes sense. Yeah, stability criteria make sense. It didn't seem like such a big deal.
But now I'm thoroughly enjoying reading the 1930's and 1940's papers and associated literature and realize that Nyquist wasn't exactly trying to formulate stuff that academics would be talking about most of a century later. He was really solving the most fundamental pressing everyday issues of electrical, radio, telegraph, and telephone engineering.
Everything he did, he did to solve a problem with real equipment in the real world. Other people were working on the same problems and made many contributions too (I recently brushed up on Black's and Bode's original papers too.)
In every single case, Nyquist seems to have come up with a fundamental truth, or diagram, or criteria, that wasn't just applicable to feedback audio amps, or wasn't just applicable to telegraphy, or wasn't just applicable to phone systems, or wasn't just applicable to long undersea cable runs, but also was a fundamental part of information theory. He established criteria and diagrams and notation that absolutely permeate all aspects of how people today think about information.
Wow. Did Bell Labs get their money's worth out of this guy or what???!!
I'm pretty quick with notation but not the brightest guy in the world at getting the notion. I could usually conquer the mechanics of math or physics long before I really grokked what it all meant. But in the context of 1920's/1930's engineering, I finally see what problems Nyquist was trying to solve, and see how absolutely amazing it is that he came up with such general principles that we use (not just talking about the principles, but with the principles, because he defined the vocabulary and how we think) today.
Tim.