Zaraθuštra), Zarathushtra Spitama or Ashu Zarathushtra, was the founder of Zoroastrianism.
He was a native speaker of Old Avestan and lived in the eastern part of the Iranian Plateau, but his birthplace is uncertain.
Zoroastrianism was the official religion of Persia (Modern Iran) and its distant subdivisions from 600 BC to AD 650.
The religion named after him is not attested historically until the 5th century BC, where it appears in Greek sources.
He is credited with the authorship of the Yasna Haptanghaiti as well as the Gathas, hymns which are at the liturgical core of Zoroastrian thinking.
Most of his life is known through the Zoroastrian texts. The Greek form of the name appears to be based on a phonetic transliteration or semantic substitution of Avestan zaraϑ- with the Greek zōros (literally "undiluted") and the Avestan -uštra with astron ("star").
In Avestan, Zaraϑuštra is generally accepted to derive from an Old Iranian *Zaratuštra-; The element half of the name (-uštra-) is thought to be the Indo-Iranian root for "camel", with the entire name meaning "he who can manage camels".
But if Zaratuštra-, meaning "[owner of the] golden camel", is correct, it is derived from old Eastern Iranian word *zar- for gold and ushtra for camel.
An Eastern Iranian origin is also suggested by the fact that the Old Persian word dar as a Western-Iranian dialect would be the equal term of Eastern Iranian zar, and Modern Persian uses the Eastern Iranian word for gold.) in Avestan zaraϑuštra was for a time itself subjected to heated debate because the -ϑ- is an irregular development: As a rule, *zarat- (a first element that ends in a dental consonant) should have Avestan zarat- or zarat̰- as a development from it.
Why this is not so for zaraϑuštra has not yet been determined.
Notwithstanding the phonetic irregularity, that Avestan zaraϑuštra with its -ϑ- was linguistically an actual form is shown by later attestations reflecting the same basis.
Zoroaster is traditionally dated 628 to 551 BC, however, some scholars have dated him much earlier, around the 10th century BC, on account of reconstruction of the Proto-Indo-Iranian language and religion.