Xerxes I (خشایارشا), was a Persian king (reigned 485 - 465 BC) of the Achaemenid dynasty. "Xerxes" is the Greek attempt to spell the Persian name Khshayarsha. In the Bible Xerxes I is known as Ahasuerus.
A son of Darius I and Atossa, the daughter of Cyrus the Great, he was appointed successor to his father in preference to his eldest half-brothers, who were born before Darius had become king. After his accession in October 485 BC he suppressed the revolt in Egypt which had broken out in 486 BC, appointed his brother Achaemenes as henchman (or khshathrapavan, satrap) bringing Egypt under a very strict rule. His predecessors, especially Darius, had not been successful in their attempts to conciliate the ancient civilizations. This probably was the reason why Xerxes in 484 BC abolished the Kingdom of Babel and took away the golden statue of Bel (Marduk, Merodach), the hands of which the legitimate king of Babel had to seize on the first day of each year, and killed the priest who tried to hinder him. Therefore Xerxes does not bear the title of King of Babel in the Babylonian documents dated from his reign, but King of Persia and Media or simply King of countries (i.e. of the world). This proceeding led to two rebellions, probably in 484 BC and 479 BC.
Darius had left to his son the task of punishing the Greeks for their interference in the Ionian rebellion and the victory of Marathon. From 483 Xerxes prepared his expedition with great care: a channel was dug through the isthmus of the peninsula of Mount Athos; provisions were stored in the stations on the road through Thrace; two bridges were thrown across the Hellespont. Xerxes concluded an alliance with Carthage, and thus deprived Greece of the support of the powerful monarchs of Syracuse and Agrigentum. Many smaller Greek states, moreover, took the side of the Persians, especially Thessaly, Thebes and Argos. A large fleet and a numerous army (some have claimed that there were over 2,000,000) were gathered. In the spring of 480 Xerxes set out from Sardis. At first Xerxes was victorious everywhere. The Greek fleet was beaten at Artemisium, Thermopylae stormed, Athens conquered, the Greeks driven back to their last line of defence at the Isthmus of Corinth and in the Bay of Salamis. But Xerxes was induced by the astute message of Themistocles (against the advice of Artemisia of Halicarnassus) to attack the Greek fleet under unfavourable conditions, instead of sending a part of his ships to the Peloponnesus and awaiting the dissolution of the Greek armament. The Battle of Salamis (September 28, 480) decided the war. Having lost his communication by sea with Asia, Xerxes was forced to retire to Sardis; the army which he left in Greece under Mardonius was in 479 beaten at Plataea. The defeat of the Persians at Mycale roused the Greek cities of Asia.
Of the later years of Xerxes little is known. He sent out Satapes to attempt the circumnavigation of Africa, but the victory of the Greeks threw the empire into a state of slow apathy, from which it could not rise again. The king himself became involved in intrigues of the harem and was much dependent upon courtiers and eunuchs. He left inscriptions at Persepolis, where he added a new palace to that of Darius, at Van in Armenia, and on Mount Elvend near Ecbatana. In these texts he merely copies the words of his father. In 465 he was murdered by his vizier Artabanus who raised Artaxerxes I to the throne.
In the Bible, more specifically in the Book of Esther, Xerxes I is mentioned by the name of Ahasuerus (Hebrew אחשורוש ’Ăxašwērôš, Achashverosh). Esther was chosen as his queen after the failed invasion in Greece. The Bible tells how Haman, feeling insulted by the Jew Mordecai, tries to kill Mordecai and many Jews, but Mordecai, through Esther and Ahasuerus, manages to reverse their fate. This story must be considered an allegory because the events it relates never occurred. The story begins in the third year of the reign of Xerxes, which would be 484 B.C. He did not have a wife named "Vashti," (or "Esther," either) then or ever (his wife at this time was Amestris, daughter of a Persian general), but "Vashti" was the name of an Elamite goddess. "Esther," too, is the name of a goddess -- it's Aramaic for "Ishtar," the chief Babylonian goddess. ("Hadassah," the name Esther's family called her, comes from the Babylonian for "bride" and was one of Ishtar's titles.) "Mordecai" is a form of the Hebrew for "Marduk," the Babylonians' chief god. "Haman" comes from the name of the Elamites' chief god, "Hamman." "Shushan" is identified with Xerxes's capital, Susa. The allegory means that Babylonian gods replaced Elamite gods in Susa in the last years of the Assyrian Empire, and it was written at a time when the Macedonians posed the kind of danger to the Jews that the story describes.