I see, in this thread, a lot of good examples wrt good python books, but the nature of the question left me to wonder. When I hear "What is the K&R of X", it makes me think of "what is the book, preferably by the creator of the language, that represent, most faithfully, the spirit of the language".
For example, compare Programming Perl (aka the Camel book) to K&R, the former is a long, didactic, journey through Perl's linguistic building blocks, while the latter is a laconic, technical, concise guide to C. I think these also embody the philosophy and nature of these languages.
Another example would be Lisp/Scheme books that tend to be academic, and theoretical.
For example, compare Programming Perl (aka the Camel book) to K&R, the former is a long, didactic, journey through Perl's linguistic building blocks, while the latter is a laconic, technical, concise guide to C. I think these also embody the philosophy and nature of these languages. Another example would be Lisp/Scheme books that tend to be academic, and theoretical.