What was the name of Alexander's elite cavalry unit?

Alexander’s elite cavalry unit was the Companion cavalry, known in Greek as the Hetairoi. It was the heavy cavalry arm of the Macedonian army and became one of the most important instruments of Alexander’s battlefield victories.

The Companions were originally drawn largely from Macedonian aristocratic families, although the force later included trusted non-Macedonian soldiers. They carried the long xyston lance, swords, armour, and helmets, and commonly attacked in a tightly organised wedge formation. Alexander often led the Royal Squadron personally.

Their usual battlefield role was the “hammer” in a hammer-and-anvil tactic. Macedonian phalangites pinned the enemy infantry in place, while the Companion cavalry struck a weakened flank or gap with a concentrated shock charge. At Granicus, Issus, and Gaugamela, this combination helped Alexander break much larger forces.

The Hypaspists were elite infantry, the phalanx was the main infantry formation, and Agema referred to a guard or elite detachment. Those terms are related to Alexander’s army but do not name his famous elite heavy cavalry corps.