Has there been any literature dealing with the question why Nietsche chose to make Zarathustra the "prophet" of his "Death of God"? in the Gay Science the madman remains unnamed, even though the parallels in thought are already noticeable.
Nietzsches background suggests, that he knew very well who Zarathustra was and during his study times several translations and commentaries on the Zoroastrian scriptures were published, e.g. by Friedrich von Spiegel. It was for sure not a mere coincidental choice but much more a decision he had thought through very well.
Are there any books or articles treating the question of "Why Zarathustra"?
Sorry for not having worded my question clearer. Nietzsches reasoning of "Why I Am Fatality" chapter 3 in Ecce Homo is known to me that is why I asked if there are any texts treating it outside of this.
I think that for merely that thought others would have been better or at least equally well suited, e.g. the whole Epicurean school, Gilgamesh, et al., and Nietzsche was surely very familiar with them. It is also questionable that the historico-critically influenced Nietzsche (see his Texts on David Friedrich Strauss in Unzeitgemässe Betrachtungen/Untimely Meditations) would have held up an early dating of Zarathustra given that the discussion of the time was mainly about whether he lived around 1200BC or 600BC (see 1st ed. of the Religion in Geschichte und Gegenwart, Art. "Parsismus", col. 1364-1382).
I strongly believe that Nietzsche also aimed at the biblical prophets when chosing Zarathustra as the prophet of the Death of God, especially since the discussion of the time was the connection between postexilic Judaism and Zoroastrism (cf. RGG1, col. 1382).