The term was contracted to Soshans in Zoroastrian tradition and came to apply to three saviour figures that were prophesied to progressively bring about the final renovation.
[1] In the Gathas, the most sacred hymns of Zoroastrianism, believed to have been composed by Zoroaster himself, the term is used as a common noun to refer to the prophet's own mission and to his community of followers, who "bring benefit" to humanity.
He is identified as the son of Vîspa.taurwairî and it is stated that he will come forth from Lake Kansaoya/Kansava and will carry the same weapon Verethragna that a number of Iranian epic heroes and kings have used in the past against various demonic foes.
Those medieval works of Zoroastrian tradition envision three future saviours, each of them a Soshans/Saoshyant, with one for the end of each thousand-year period that comprise the last 3,000 years of the world (these three millennia follow the "millennium of Zoroaster").
The medieval works also transmit a tradition in which the three future saviours are mythologised as born of maidens, conceived while their mothers bathed in a lake that miraculously preserved the seed of the prophet Zoroaster himself.
Eventually, Ahura Mazda will triumph, and his agent Saoshyant will resurrect the dead, whose bodies will be restored to eternal perfection, and whose souls will be cleansed and reunited with God.