Cyrus II, nigh legendary first king of Persia, nearly wasn’t. He was born to Cambyses, king of Anshan, and Mendane, daughter of King Astyages of Media, in either 600 BCE or 576 BCE. (Ancient calendars being what they were, subsequent historians aren’t quite sure which.) According to the tales, Astyages was convinced by repeated dreams that his grandson would someday overthrow him. Since power was thicker than blood for the Median king, he summoned his pregnant daughter and insisted the child be killed as soon as it was born. The task was delegated to a shepherd, Mithradates, who did not kill the infant Cyrus and instead raised him as one of his own sons. Herodotus claimed the ruse was uncovered when Cyrus reached the age of 10 because his behavior was “too noble.” Caring for neither a civil war nor conflict with Cambyses, Astyages sent Cyrus back to his biological parents in Persia.
Astyages was right to be concerned by his grandson. Although his father did not die until 551 BCE, Cyrus had already ascended to the throne in 559 BCE. Like his predecessors, Cyrus was forced to recognize Median overlordship … at least until a surprise attack against his grandfather in 553 BCE. Rallying the tribes—including the Achaemenian relations of his wife Cassandane—Cyrus defeated the Medians in several pitched battles, eventually capturing the capital at Ecbatana in 549 BCE. Accepting the crown of Media in 546 BCE, Cyrus proclaimed himself “King of Persia.” History doesn’t record what became of Astyages, but it is considerably less likely he was adopted by a shepherd tasked with his murder.
The conquest of Media was only the start of Cyrus's bloodshed. Astyages had been allied to Nabonidus of Babylon, Amasis of Egypt, and his brother-in-law Croesus of Lydia. Within a year of Astyages’s defeat, the Lydians were on the march. Cyrus levied troops from throughout his lands and fought Lydian forces to stalemate at Pteira. He next attacked the Lydian capital at Sardis, where he routed the vaunted Lydian cavalry by putting camels in the front lines. According to Herodotus, Cyrus spared Croesus and made him a trusted advisor—but the 'Nabonidus Chronicle' disagreed, claiming Cyrus double-crossed the fallen king and had him slain.
After putting down a revolt in Media by the official transporting Croesus’s supposed vast treasury to Cyrus’s palace, the Persians proceeded to capture Elam’s capital on the way into Babylonia. Around early October 540 BCE, Cyrus finally forced the Babylonians to battle near their city of Opis on the banks of the Tigris, just north of Babylon. The Babylonians were routed, Nabonidus fled, and Cyrus negotiated a truce, thus entering Sippar unopposed. Reaching Babylon, Cyrus used an existing great ditch to divert the Euphrates and walk his troops across the riverbed. They invaded the city at night against meager defenders and "detained" Nabonidus. (The 'Nabonidus Chronicles' said he was exiled and allowed to live out his life in nearby Carmania, where Cyrus could keep an eye on him.)
Having added fallen Babylonia to his now extensive holdings, Cyrus also acquired various pieces of its empire in Syria, Judea, and Patraea. Feeling quite pleased with himself, Cyrus proclaimed himself “King of Babylon, King of Sumer and Akkad, King of the Four Corners of the World.” This is known from the (in)famous “Cyrus Cylinder,” etched and laid in the foundations of the Esagila temple dedicated to Marduk, the primary Babylonian god. The cylinder denounces Nabonidus as impious and depicts Cyrus as “pleasing to Marduk.” It also details how Cyrus improved the lives of the Babylonians, restored temples and cults previously outlawed, and repatriated displaced peoples—such as his 538 BCE decree allowing captive Jews to return to Judah.
Although some historians and other wishful thinkers have asserted that the cylinder represents an early form of human rights charter, most scholars portray it in the context of the long-standing Mesopotamian tradition of new rulers beginning their reign with declarations of largesse and reforms, especially after the fall of an unpopular king.
Cyrus spent his last years putting the Achaemenid dynasty on a sound footing. To avoid unrest in newly conquered lands, he allowed most nobles to become government officials and gave them equal status with Persian nobility. He left the institutions in conquered lands alone, allowing the people to largely govern themselves, and didn’t meddle with local religions, which proved an exceedingly wise decision. Cyrus also built a series of fortified towns along the eastern borders to protect his empire from the nomads of Central Asia, and formed a streamlined central government at his capital at Pasargadae which administered the regions through local elders. In short, he successfully organized the vast territory he had conquered into something resembling an empire.
The details of Cyrus's passing vary. According to Herodotus (whose tales are largely just that), a backstabbing Cyrus met his fate at the hands of the warrior-queen Tomyris of the Scythians. (That theory of his death is recounted in Tomyris's Civilopedia entry.) Ctesias, even less reliable than Herodotus, wrote in his 'Persica' that Cyrus was killed while putting down resistance from the Derbices. Berossus claims the Persian king met his death while fighting against Dahae archers northwest of the headwaters of Syr Darya. A final alternative is that from Xenophon’s Cyropaedia, which says that Cyrus died peacefully resting at his capital. Whatever the case, Cyrus’s remains were interred in a limestone tomb in Pasargadae (which tends to give credence to Xenophon’s account), which many believe still exists in the ruins of that great city.