The notion that Zoroastrian monotheism influenced the Old Testament authors is a very widespread idea. It is an attractive idea because it fits so well with the theory that the Torah was compiled during the Persian period. It is also evident that Jews held the most famous Achaemenid kings, Cyrus and Darius, in high regard and there is a lot of evidence of Persian influences in Judaism; so, the influence of Zoroastrianism was very plausible. However, the theory of the monotheistic influence of Zoroastrianism on Judaism during the period of the Achaemenid kings breaks down on closer examination. But, the story of how this became such a pervasive idea illuminates some of the biggest problems in how history was created over the last 100 or so years. As usual, it was a story shaped by political ambition and blind acceptance of religious traditions, rather than an honest look at the evidence.
The problem with understanding the development of Zoroastrianism began in the 19th century with the scholarly acceptance of Zoroaster as the prophet who began the religion. The most prominent western scholars thought it preposterous to question the existence of the prophet (Skjærvo̵ 1997). The only question they debated was when Zoroaster lived. This question continues to be debated and the dates range wildly between 1200 BCE to 600 BCE. However, there is simply no evidence that Zoroaster was a real person and the claims that he existed are from centuries after his supposed life. As with all other legendary prophets, it is plausible that there was some guy named Zoroaster; but, his existence is unnecessary for explaining the origin of the faith.
The early archaeological work in Iran seemed to point to very early evidence of Zoroastrianism. But, the interpretation of that evidence was extremely influenced by the political climate in Iran during the 20th century, under the rule of the shahs. Reza Kahn was not a very religious person; but, he promoted nationalism in Iran to glorify and legitimize his rule. (Abdi 2001) As the preferred ruler of Iran by western countries, western scholars had little interest in questioning his promotion of a national history of Iran that glorified Zoroaster and undermined Islam. The Iranian government and western governments, particularly the British, were happy with the overt nationalism promoted through archaeology in Iran. So, even school children in America learned that Zoroastrianism was the first monotheistic religion.
Recent reexamination of the archaeological evidence claimed as demonstrating proto-Zoroastrian religious practices shows the flaws in the earlier theory. Sites interpreted as Zoroastrian fire temples are now understood as simply being rather typical pagan temples of the time and not as evidence of monotheism (Shenkar 2007). The earlier notion that Zoroastrian monotheism was “corrupted” with polytheistic influences from the Elamites and Mesopotamians no longer makes sense. It is evident that Zoroastrianism evolved from polytheistic beliefs, in much the same way as monotheism evolved across West Asia and along the same time line. The Zoroastrian texts were first compiled under the Sasanians during the 3rd century CE, when the kings were instituting theocratic government (Daryaee 1995). Just as the Roman emperors found monotheism to be politically useful, the Sasanians promoted the trend in Zoroastrianism.
This short summary of how the history of Zoroastrianism developed demonstrates that no history can simply be read and accepted at face value, particularly when it is a history of a religion. Religious histories are always three dimensional, influenced by both ancient and modern political factors.
Abdi, Kamyar. "Nationalism, Politics, and the Development of Archaeology in Iran." American Journal of Archaeology 105 (Jan. 2001): 51-76.
Daryaee, Touraj. "National History or Keyanid History?: The Nature of Sasanid Zoroastrian Historiography." Iranian Studies 28, no. 3/4 (Summer-Autumn 1995): 129-141.
Shenkar, Michael. "Temple Architecture in the Iranian World." Iran & The Caucasus 11, no. 2 (2007): 169-194.
Skjærvo̵, P. Oktor. "Review: The State of Old Avestan Scholarship." Journal of the American Oriental Society 117, no. 1 (Jan.-Mar. 1997): 103-114.
I was inspired to write this article by a question that came up during my radio interview with Brian Magee on the Appreciate Your Mind program on KNDS, 96.3 FM in Fargo, ND. I give some other reasons for why the Zoroastrian monotheism was an unlikely inspiration for the Old Testament authors during the interview, as well as discuss a number of other issues. You can listen to a podcast of the show here: http://appreciateyourmind.podomatic.com/