Who wrote the philosophical work Thus Spoke Zarathustra?

Nietzsche, between 1883 and 1885, and he wrote it as something between a novel and scripture - a prophet comes down from a mountain to tell people that God is dead and is largely ignored. He thought it his most important book and had the fourth part printed privately in forty copies because no publisher wanted it.

God is dead is the most misquoted line in philosophy. It is not a triumphant announcement but a diagnosis, and it comes with the observation that we have killed him and that the consequences are not going to be pleasant - if the foundation of European morality has gone, the morality does not simply carry on unsupported, and Nietzsche expected the twentieth century to be violent as a result.

He collapsed in Turin in 1889, reportedly after seeing a horse being whipped, and spent his last eleven years insane and cared for by his sister Elisabeth. She was an antisemite and a German nationalist, and she edited his unpublished notes into a book he never wrote, cutting what she disliked and shaping the rest - which is how a philosopher who despised antisemitism and German nationalism became a Nazi favourite. Scholars spent decades disentangling it, and the damage to his reputation lasted most of a century.