Answer: The Persians had one official religion, Zoroastrianism, while the polytheistic Greeks worshipped many different gods in different ways.
Step-by-step explanation:
Zoroastrianism was the Persian faith and probably the very first monotheistic religion and one of the earliest faiths still in existence. Unto the Muslim conquering of Persia, Zoroastrianism was the official creed of three Persian dynasties.
Ancient Greek religion was polytheistic, with several gods and goddesses in a hierarchy that had Zeus as the king of all.