According to the Behistun Inscription, pseudo-Smerdis ruled for seven months before being overthrown by Darius I in 521 BCE. The "Magi", though persecuted, continued to exist, and a year following the death of the first pseudo-Smerdis (named Gaumata), had a second pseudo-Smerdis (named Vahyazdāta) attempt a coup. The coup, though initially successful, failed.
Whether [[Cyrus the Great|Cyrus II ]] was a Zoroastrian is subject to debate. It did however influence him to the extent that it became the non-imposing religion of his empire, and its beliefs would later allow Cyrus to free the Jews from captivity (and allow them to return to Judea) when the emperor took Babylon in 539 BCE. Whether Darius I, though certainly a devotee of Ahura Mazda (as attested to several times in the Behistun inscription), was a follower of Zoroaster has not been conclusively established, since a devotion to Ahura Mazda was (at the time) not necessarily an indication of an adherence to Zoroaster's teaching.
Darius I and later Achaemenid dynasty, though acknowledging their devotion to Ahura Mazda in inscriptions, appear to have permitted religions to coexist. Nonetheless, it was during the Achaemenid period that Zoroastrianism gained momentum, and a number of the Zoroastrian texts (that today are part of the greater compendium of the Avesta) have been attributed to that period. It was also during the (later) Achaemenid era that many of the divinities and divine concepts of proto-Indo-Iranian religion(s) were incorporated in Zoroastrianism, in particular, those to whom the days of the month of the Zoroastrian calendar are dedicated. That religious calendar, which is still in use today, is itself (to some extent) an Achaemenid-era development. Those divinities, the ''yazata''s, are present-day Zoroastrianism's angels. (Dhalla, 1938).