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 Pars (Persis) and was formed under Cyrus the Great. Successive states in Iran before 1935 are collectively called the Persian Empire by Western historians.
Prior to this, Persia's earliest known kingdom was the indigenous proto-Elamite Empire whose rule was limited to western provinces of what is modern-day Iran, while the indigenous Jiroft Kingdom ruled the eastern provinces. In the 1st millenium BC, with the arrival of Indo-European Aryans on the Iranian plateau, indigenous kingdoms in Iran successively fell to the outnumbering Aryans in wars of settlement.
The first kingdom founded by Aryans in Iran was the Median empire, which completely ruled the Iranian plateau.