Cyrus was Zoroastrian, wasn't he? That's a small but significant threat to the Arab/Moslem infestation which rules Iran.
For now.
Actually we don't know what religion Cyrus believed in, because he wouldn't impose it on anyone! Darius I was the first Persian king we know of who openly practiced Zoroastrianism. Cyrus could have been Zoroastrian, or he could have followed the old Indo-Iranian paganism, or who knows what? The assistant pastor of my church has even suggested that Cyrus was a secret believer in the God of Israel, which I guess is as close to converting to Judaism as one could do in those days.