The name of the founding Prophet of Zoroastrianism is not Zoroaster, which is a Greek transliteration of the name, but Zarathushtra, which means, in ancient Iranian, "yellow camel." (zara = yellow, ushtra = camel). An alternate reading is "old camel." Animals such as camels and horses were essential and even sacred to the people of Zarathushtra's age, and thus a name containing one of these animals marks a person as important. A similar naming practice occurred among the ancient Greeks where names containing "-ippos" or horse denoted high birth - such as Philippos (lover of horses), Aristippos (best horse), or Xanthippos (yellow horse).

The later Zoroastrians, perhaps embarrassed by their prophet's primitive-sounding name, said that the name meant "Golden Light," deriving their meaning from the word zara and the word ushas, light or dawn. There is no doubt about Zarathushtra's clan name, which is Spitama - perhaps meaning "white." Zarathushtra's father was named Pouruchaspa (many horses) and his mother was named Dughdova (milkmaid). His birthday is celebrated on March 26, as part of the Iranian New Year Festival.

No one knows where or when the Prophet was born. Some legends place his birth in western Iran, perhaps near Tehran; others, which are somewhat more likely due to the eastern Iranian language of his poetry, place his birthplace in the east. As for the date of his birth, it has been since ancient times a matter of controversy. Greek sources placed him as early as 6000 B.C., a reckoning derived from poorly transmitted Zoroastrian legends; few if any scholars take that date seriously. The traditional Zoroastrian date for Zarathushtra's birth and ministry is around 600 B.C. This is derived from a Greek source that places him "300 years before Alexander" which would give that date; other rationales for the 600 BC date identify the King Vishtaspa of Zarathushtra's Gathas with the father of the Persian King Darius, who lived around that time.

As the linguists of both Europe and India worked on the Gathas, however, it became clear that the language of the Gathas attributed to Zarathushtra was far older than the language spoken in Iran at the time of King Darius' father. Gathic Avestan was very close to the Sanskrit of the Indian Rig-Vedas, which can be dated from the period 1500-1200 BC. This would mean that Zarathushtra lived far earlier than the "traditional" date. Some scholars have said that the 600 BC date is still plausible if Gathic Avestan was actually an artificially preserved sacred language, somewhat like Latin, which continued in literature and rituals thousands of years after it had ceased to be spoken.

Recent work by Martin Schwartz and Almut Hintze tends to discount this theory, as the linguists show that the Gathas are not the work of an academic writing in a dead language; they show all the signs of poetry composed and recited in an oral tradition, similar to the heroic poetry of Homer or the Rig-Vedas. These studies would confirm the earlier date for Zarathushtra.

The problem of Zarathushtra's time will never be solved, unless some improbable archaeological find turns up. Most scholars agree on a time-frame for Zarathushtra which could be as early as 1700 B.C. or as late as 1000 B.C.

Zarathushtra received his prophetic calling in about his thirtieth year, in which he envisioned God through Vohu Manah, or "Good Mind." His prophecies were not foretelling of the future, but prophecy in the sense of the later Hebrew prophets: revolutionary messages of religious purity and social justice, speaking out against corrupt priests and potentates.

There is very little biographical material in the Gathas. What is there indicates that Zarathushtra was cast out of his original home, wherever that was, and forced to wander, along with his followers and their animals. Yasna 46 begins with a sad verse about this:

"To what land should I turn? Where should I turn to go?
They hold me back from folk and friends.
Neither the community I follow pleases me,
nor do the wrongful rulers of the land...
I know... that I am powerless.
I have a few cattle and also a few men."
(Jafarey translation)

He and his followers wandered until they found a sympathetic friend in King Vishtaspa, who was not the father of King Darius but an earlier ruler of the same name, who may have lived in eastern Iran or in Bactria, modern Afghanistan. There, Zarathushtra won over the king, and his court, and became the court prophet.

Zarathushtra is said to have had six children, three boys and three girls. This is not exact information, since the number and gender equals that of the six Amesha Spentas and may be only symbolic. But the last Gatha is composed for the marriage of Zarathushtra's daughter Pouruchista (Full of Wisdom) so he is known to have had at least one child. Zarathushtra, in the legends, had three wives (in sequence) of whom the last was Hvovi (Good Cattle) the daughter of King Vishtaspa's prime minister. Thus Zarathushtra married into the king's court; Pouruchista, in turn, married the prime minister.