Xerxes, (519?–465 B.C.), a king of Persia, also called Xerxes the Great. In the Biblical book of Esther he is called Ahasuerus. Xerxes was the son of Darius and grandson of Cyrus the Great. He became king in 485 B.C. when the Persian empire was a world power. He achieved his first victory as a military leader by suppressing a revolt in Egypt.

Starting in 483 B.C. Xerxes planned a land and sea campaign to seize Greece. His forces dug a canal across the easternmost peninsula of Greece near Mount Athos, built supply depots for the line of march, and constructed two bridges of boats across the Hellespont (Dardanelles). In 480 Xerxes launched his attack. The Greek historian Herodotus stated that Xerxes had nearly 2,000,000 combat troops, including camel units and a navy of 1,200 ships. Modern historians estimate the army at 250,000 and the fleet at 1,000, including 600 battle triremes (warships with three banks of oars).

The Persian army defeated the Greeks at Thermopylae and seized Athens (480 B.C.). The conquest of Greece seemed near. But, under the direction of Themistocles, the newly strengthened Greek navy routed the Persian fleet at the battle of Salamis while Xerxes watched from a seaside height. His navy destroyed, Xerxes retired to Persia. The army he left in Greece was defeated at Plataea in 479. A few years later Xerxes was killed by the captain of his bodyguard. He was succeeded by his son, Artaxerxes I.