This is the work of Friedrich Nietzsche, the great German philosopher of the late 1800's. This book pronounces that God is dead, and that poeple should concern themselves with mankind not God. Nietzsche is often cited as the beginning of Existentialism.

Also Sprach Zarathustra is also the title of composer Richard Strauss's classical piece used in 2001: A space Oddysey. You know, the one with the brass and drums...