Perhaps Nietzsche's most enduringly popular work with non-academics is Thus Spoke Zarathustra. Nietzsche uses the prophet, Zarathustra, from ancient Persia to speak for himself in it (aka Zoroaster). The last men proclaim, "We have invented happiness," and they blink, says Zarathustra. The crowd applauds and requests that Zarathustra change them into these last guys. A tightrope walker starts crossing the town's two towers just then. The change or continued growth of humanity is the main theme of the work, as conveyed in Zarathustra's opening speech to the populace after emerging from his mountain cave. Zarathustra's own struggle and transformation are also part of the narrative that is developing in the text.