Cyrus I, fl mid 7th C. BC, was the third Achaemenid king of Persis, then part of the wider Median Empire. The dynasty was said to have been founded by Achaemenes, who possibly ruled in the early seventy century BC, under Median control. He was succeeded by his son Teispes, who ruled during a period of Median weakness. Teispes was said to have extended his kingdom, but then at his death split it between his sons Ariaramnes and Cyrus I.
Cyrus I inherited the western part of Persis, also known as Anshan. Like his father he appears to have been free of Median control, but it is possible that he had to acknowledge Assyrian rule. He may have been the Persian king who sent aid to Shamash-shum-ukin of Babylonian during a failed revolt against Assyria in 651 BC. Assyrian documents record a king of Persia who swore allegiance to Ashurbanipal in the aftermath of the Assyrian destruction of Elam in 642-639 BC, sending a son named Arukku in the Assyrian sources to pay tribute at Nineveh. This may have been Cyrus I, attempting to gain support against his Median neighbours or to prevent any attack by the Assyrians, who bordered his realm.
Cyrus I was succeeded by his son Cambyses I, the father of Cyrus II the Great, founder of the Persian Empire.