Generally, the earliest entity considered the Persian Empire is Persia's Achaemenid Empire (648-330 BC) a united Aryan-indigenous Kingdom that originated in the region known as Parac (Strong's H6539, Heb. פרס) and was formed under Cyrus the Great. Successive states in Iran before 1935 are collectively called the Persian Empire by Western historians.
Persia = "pure" or "splendid"
1) the empire Persia; encompassed the territory from India on the east to Egypt and Thrace on the west, and included, besides portions of Europe and Africa, the whole of western Asia between the Black Sea, the Caucasus, the Caspian and the Jaxartes on the north, the Arabian desert, the Persian Gulf and the Indian Ocean on the south
a) Persia proper was bounded on the west by Susiana or Elam, on the north by Media, on the south by the Persian Gulf and on the east by Carmania Persian = see Persia "pure" or "splendid"
2) the people of the Persian empire