Cyrus I was King of Anshan from c. 600 to 580 BC or according to others from c. 652 to 600 BC.

He was an early member of the Achaemenid dynasty. He was apparently a grandson of its founder Achaemenes of Anshan and son of Teispes of Anshan. Teispes' sons reportedly divided the kingdom among them after his death. Cyrus reigned as King of Anshan while his brother as King Ariaramnes of Persia.

The chronological placement of this event is uncertain. This is due to his suggested but still debated identification with the monarch known as "Kuras of Parsumas". Kuras is first mentioned c. 652 BC. At that year Shamash-shum-ukin, King of Babylon (668 - 648 BC) revolted against his older brother and overlord Ashurbanipal, King of Assyria (668 - 627 BC). Kuras is mentioned being in a military alliance with the former. The war between the two brothers ended in 648 BC with the defeat and reported suicide of Shamash-shum-ukin.

Kuras is mentioned again in 639 BC. At that year Ashurbanibal managed to defeat Elam and became overlord to several of its former allies. Kuras was apparently among them. His elder son "Arukku" was reportedly sent to Assyria to pay tribute to its King. Kuras then seems to vanish from historical record. His suggested identification with Cyrus would help connect the Achaemenid dynasty to the major events of the 7th century BC.

Ashurbanipal died in 627 BC. Cyrus presumably continued paying tribute to his sons and successors Ashur-etil-ilani (627 - 623 BC) and Sin-shar-ishkun (623 BC - 612 BC). They were both opposed by an alliance led by Cyaxares of the Medes (633 - 584 BC) and Nabopolassar of Babylon (626 - 605 BC). In 612 BC the two managed to capture the Assyrian capital Nineveh. This was effectively the end of the Assyrian Empire though remnants of the Assyrian army under Ashur-uballit II (612 - 609 BC) continued to resist from Harran.

Media and Babylonia soon shared the lands previously controlled by the Assyrians. Anshan apparently fell under the control of the former. Cyrus is considered to have ended his days under the overlordship of either Cyaxares or his son Astyages (584 BC - 550 BC). Cyrus was succeeded by his son Cambyses I of Anshan. His grandson would come to be known as Cyrus the Great, creator of the Persian Empire.

It has been noted that this account of his life and reign would place his early activities more than a century before those of his grandson. This would place his fathering of Cambyses very late in life and his death at an advanced age. It has been argued that Kuras and Cyrus I were separate figures of uncertain relation to each other. The later would have then reigned in the early 6th century BC and his reign would seem rather uneventful. Due to the current lack of sufficient records for this historical period it remains uncertain which theory is closer to the facts.