Nietzsche, along with other historians and thinkers, attributed the first articulation of the dichotomy between good and evil to the Persian prophet Zarathustra. In his autobiography Ecce Homo, Nietzsche explains why he chose Zarathustra as the mouthpiece for the philosophical teachings presented in this book:

“Zarathustra was the first to see in the struggle of good and evil the true driving-wheel in the machinery of things—the translation of morality into the metaphysical, as strength, cause, goal in itself, is his doing […] Zarathustra created the disastrous error that is morality: thus he must also be the first to acknowledge the mistake.”
—Ecce Homo, “Why I Am a Destiny,” section 3