The prophet Zoroaster was the reformer who transformed Persian
polytheism into the first monotheism. Although little is known about
the old Persian polytheism, apparently some of the old gods were
demoted and retained as angels in Zoroaster’s synthesis.
The struggle between good and evil occupies center stage in the
Zoroastrian worldview. The god of light and the upper world,
Ohrmazd or Ahura Mazda (Wide Lord), and his angels are locked in a
cosmic struggle with the god of darkness and the lower world, Angra
Mainyu or Ahriman (Evil Spirit), and his demons.
The oldest angels in the Zoroastrian system are the six (sometimes
seven) holy immortals, often identified as archangels. The holy
immortals play an important role in the foundation of the faith,
revealing the true religion to Zoroaster in a series of visions. As
Zoroastrianism developed, the number of celestial beings multiplied,
leading some observers to remark that the old polytheistic system had
unwittingly been revived in the later stages of this religious tradition.
At some point, a new class of angel, the yazatas (“worshipful
ones”), emerged. They became so important that they seemed to
eclipse Ahura Mazda himself. Chief among the yazatas was Mithra,
the god/angel of light and truth, the mediator between earth and
heaven, as well as the preserver and judge of this world. Other new
angels, some of them transparently former gods of the old Indo-European
pantheon, were Haoma, angel of the sacred intoxicant; Vata (or
Vayu), who rules the winds; and Verethragna, the Persian equivalent
of the Indian god Indra.