Hydarnes the Younger

[1][2] On the first day of the Battle of Thermopylae, Hydarnes led the Immortals against the phalanx of Spartans under Leonidas I, but an attempt to break through failed.

[3] On the second day, a local resident named Ephialtes betrayed the Greeks by telling the Persians about a hidden goat path around Thermopylae.

This enabled Hydarnes and his Immortals to pass behind the Spartans, Thespians and Thebans and, as a result, defeat them.

[4] After the Persians were defeated at the Battle of Salamis, Xerxes I decided to return to Asia leaving a large army under Mardonius which wintered in Thessaly.

So Xerxes tasked Hydarnes with the responsibility of getting the Persian army back over the Hellespont to Asia.