Cyrus II of Persia (c. 600–530 BC; Old Persian: 𐎤𐎢𐎽𐎢𐏁 Kūruš), commonly known as Cyrus the Great, was the founder of the Achaemenid Empire, the first Persian empire. Under his rule, the empire embraced all of the previous civilized states of the ancient Near East, expanded vastly and eventually conquered most of Western Asia and much of Central Asia. Spanning from the Mediterranean Sea and Hellespont in the west to the Indus River in the east, the empire created by Cyrus was the largest the world had yet seen. At its maximum extent under his successors, the Achaemenid Empire stretched from parts of the Balkans (Eastern Bulgaria–Paeonia and Thrace–Macedonia) and Southeast Europe proper in the west to the Indus Valley in the east.

The reign of Cyrus lasted about thirty years; his empire took root with his conquests of the Median Empire, then the Lydian Empire and eventually the Neo-Babylonian Empire. He also led an expedition into Central Asia, which resulted in major campaigns that were described as having brought "into subjection every nation without exception". Cyrus did not venture into Egypt, and was alleged to have died in battle while fighting the Massagetae, an ancient Eastern Iranian nomadic tribal confederation, along the Syr Darya in December 530 BC. However, Xenophon claimed that Cyrus did not die in battle and returned to the Achaemenid ceremonial capital of Persepolis again. He was succeeded by his son, Cambyses II, who managed to conquer Egypt, Nubia and Cyrenaica during his short rule.

Known as Cyrus the Elder (Greek: Κῦρος ὁ Πρεσβύτερος, translit. Kŷros ho Presbýteros) to the Greeks, he was well-known for having respected the customs and religions of the lands he conquered. He was important in developing the system of a central administration at Pasargadae governing satraps in the empire's border regions, which worked very effectively and profitably for both rulers and subjects. The Edict of Restoration, a proclamation attested by a cylinder seal in which Cyrus authorized and encouraged the return of the Israelites to the Land of Israel following his conquest of the Neo-Babylonian Empire, is described in the Bible and likewise left a lasting legacy on the Jewish religion due to his role in ending the Babylonian captivity and facilitating the Jewish return to Zion. According to Isaiah 45:1 of the Hebrew Bible, God anointed Cyrus for this task, even referring to him as a messiah (lit. 'anointed one'); Cyrus is the only non-Jewish figure in the Bible to be revered in this capacity.

Cyrus is also recognized for his achievements in human rights, politics, and military strategy, as well as his influence on both Eastern and Western civilizations. The Achaemenid influence in the ancient world would eventually extend as far as Athens, where upper-class Athenians adopted aspects of the culture of the ruling class of Achaemenid Persia as their own. Having originated from Persis, roughly corresponding to the modern-day Fars Province of Iran, Cyrus has played a crucial role in defining the national identity of modern Iran. He remains a cult figure amongst modern Iranians, with his tomb serving as a spot of reverence for millions of people. In the 1970s, the last Shah of Iran, Mohammad Reza Pahlavi, identified Cyrus' famous proclamation inscribed onto the Cyrus Cylinder as the oldest-known declaration of human rights, and the Cylinder has since been popularized as such. This view has been criticized by some Western historians as a misunderstanding of the Cylinder's generic nature as a traditional statement that new monarchs make at the beginning of their reign.