Zarathustra (also Zoroaster c.1200 BCE ?) was an ancient Persian prophet who fled his homeland because of his controversial religious convictions. He ended up in eastern Iran under the protection of King Vishtaspa, who embraced his teachings.
The surviving scripture we have today is somewhat fragmentary, seemingly contradictory in places and only a part of the original.
Classical Greek writers called Zarathustra Zoroastres.¹
The Romantic German composer Richard Strauss’ Also Sprach Zarathustra, used in the soundtrack for Stanley Kubrick’s film 2001: A Space Odyssey, was influenced by Friedrich Nietzsche‘s philosphical work, Thus Spoke Zarathustra, which itself was influenced by the Persian prophet.
Today, the Bahai faith recognizes Zoroaster as a manifestation of God, along with several other prominent religious teachers. While this kind of thinking is no doubt well-intentioned, it runs the risk of watering down real differences among religions.
¹ From Wikipedia: Zoroaster’s name in his native language, Avestan, was probably Zaraϑuštra. His English name, “Zoroaster”, derives from a later (5th century BCE) Greek transcription, Zōroastrēs (Ζωροάστρης), as used in Xanthus‘s Lydiaca (Fragment 32) and in Plato‘s First Alcibiades (122a1). This form appears subsequently in the Latin Zōroastrēs and, in later Greek orthographies, as Zōroastris. The Greek form of the name appears to be based on a phonetic transliteration or semantic substitution of the Avestan zaraϑ- with the Greek zōros (literally “undiluted”) and the Avestan -uštra with astron (“star“). See http://en.wikipedia.org/wiki/Zoroaster