Which Persian king led the invasion at the Battle of Thermopylae? Xerxes I led the Persian invasion. He was the Achaemenid ruler who launched the second major Persian invasion of Greece in 480 BC, continuing plans begun by his father, Darius I.
Darius had initiated the earlier invasion after Athens and Eretria supported the Ionian Revolt, but he died in 486 BC before carrying out a new expedition. Xerxes first suppressed a revolt in Egypt and then organized an enormous campaign against Greece. His preparations included stockpiling supplies, building pontoon bridges across the Hellespont, and cutting a canal through the Athos peninsula for the fleet.
At Thermopylae, Xerxes faced a Greek force led by Leonidas of Sparta. The narrow pass allowed the defenders to hold off repeated Persian assaults for several days. The position was eventually outflanked after Ephialtes showed Persian troops a mountain route behind the Greek lines.
Xerxes captured Athens after Thermopylae, but his campaign ultimately failed to conquer Greece. The Greek naval victory at Salamis forced him to withdraw much of his army, and the following year the Persian commander Mardonius was defeated at Plataea.