Xerxes I, commonly known as Xerxes the Great, was a Persian ruler who served as the fourth King of Kings of the Achaemenid Empire, reigning from 486 BC until his assassination in 465 BC. He was the son of Darius the Great and Atossa, a daughter of Cyrus the Great. In Western history, Xerxes is best known for his invasion of Greece in 480 BC, which ended in Persian defeat. Xerxes was designated successor by Darius over his elder brother Artobazan and inherited a large, multi-ethnic empire upon his father's death. He consolidated his power by crushing revolts in Egypt and Babylon, and renewed his father's campaign to subjugate Greece and punish Athens and its allies for their interference in the Ionian Revolt. In 480 BC, Xerxes personally led a large army and crossed the Hellespont into Europe. He achieved victories at Thermopylae and Artemisium before capturing and razing Athens. His forces gained control of mainland Greece north of the Isthmus of Corinth until their defeat at the Battle of Salamis. Fearing that the Greeks might trap him in Europe, Xerxes retreated with the greater part of his army back to Asia, leaving behind Mardonius to continue his campaign. Mardonius was defeated at Plataea the following year, effectively ending the Persian invasion.

King of Kings was a ruling title employed primarily by monarchs based in the Middle East. Although most commonly associated with Iran, especially the Achaemenid and Sasanian Empires, the title was originally introduced during the Middle Assyrian Empire by king Tukulti-Ninurta I and was subsequently used in a number of different kingdoms and empires, including the aforementioned Persia, various Hellenic kingdoms, India, Armenia, Georgia, and Ethiopia.