Michael Byrne in a Vice article:
When techno-human civilization has finally collapsed, perhaps the result of a nuclear war programmed in C or the result of a bacterial superstrain isolated by software implemented in C, and we have been returned to our caves to gnaw bones and fight over rotten meat, there will still be a program written in C executing somewhere.
All of this isn't just because a lot of people really like coding in C, though it's been estimated that almost 20 percent of all coders use the language (see below). C is far deeper than what we normally think of when we think of "programming language." There are languages that we consider to be more or less foundational—Java, Python, Ruby, Lisp, etc.—which are the very general-purpose languages. C is also general-purpose programming language, but the difference is that C has become the de facto language of machines themselves, whether it's a five dollar microcontroller or a deep-space probe.
It is the closest thing we have to a defacto standard in the computer world.