I forgot to say how right SL is on the god-king bit — the Persians did not have this as they worshipped Ahura Mazda.
Hate to disagree, but it's just not that simple. There is considerable disagreement about whether the Persians of Xerxes' time were really Zoroastrians in the later sense of the term. They seem to have had other gods and goddesses, though it's not clear whether these were part of a pantheon or were demigods or angels. Somewhat similar to medieval Christianity with all its saints. An outsider, or even many of the uneducated at the time, might have thought these were gods.
In any case, the position of the Persian shahs was very darn similar to a God-King. The Greeks certainly picked up the idea from the Persians.
It is certain that the later Parthians and others heavily influenced by the Persians had other gods such as Mithras.
Full-bore monotheistic Zoroastrianism doesn't seem to have come in till the Sassanids of 225 AD on. And this may have been largely in response to Christianity.