Darius I (Old Persian: Dārayava(h)uš, New Persian: داریوش Dāryuš; Hebrew: דָּרְיָוֶשׁ, Modern: Darəyaveš, Tiberian: Dāryāwéš; c. 550–486 BCE), commonly known as Darius the Great, was the fourth Persian King of Kings of the Achaemenid Empire. He ruled the empire at its peak, when it included much of West Asia, the Caucasus, parts of the Balkans (Thrace-Macedonia, and Paeonia), most of the Black Sea coastal regions, parts of the North Caucasus, Central Asia, as far as the Indus Valley in the far east and portions of north and northeast Africa including Egypt (Mudrâya), eastern Libya, and coastal Sudan.
Darius ascended the throne by overthrowing Gaumata, a claimed usurper. The new king met with rebellions throughout his kingdom and quelled them each time. A major event in Darius's life was his expedition to punish Athens and Eretria for their aid in the Ionian Revolt and subjugate Greece. Although ultimately ending in failure at the Battle of Marathon, Darius succeeded in the re-subjugation of Thrace, expansion of the empire through the conquest of Macedon, the Cyclades and the island of Naxos and the sacking of the city of Eretria.
Darius organized the empire by dividing it into provinces and placing satraps to govern it. He organized Achaemenid coinage as a new uniform monetary system, along with making Aramaic the official language of the empire. He also put the empire in better standing by building roads and introducing standard weights and measures. Through these changes, the empire was centralized and unified. Darius also worked on construction projects throughout the empire, focusing on Susa, Pasargadae, Persepolis, Babylon, and Egypt. He had the cliff-face Behistun Inscription carved to record his conquests, an important testimony of the Old Persian language.
Darius is mentioned in the biblical books of Haggai, Zechariah, and Ezra–Nehemiah.
Source: Wikipedia, "Darius the Great", available under the CC-BY-SA License.