The term 'King Persian' refers to two of the most famous kings in Persian history, DARIUS and CYRUS. DARIUS was the sixth king of the Achaemenid Empire, ruling from 522 to 486 BC. He is known for his administrative reforms and for expanding the empire to its greatest extent. CYRUS was the founder of the Achaemenid Empire, ruling from 550 to 530 BC. He is remembered for his military conquests and for his policy of religious tolerance.