The Companions were the elite heavy cavalry of the Macedonian army from the time of King Philip II of Macedon, achieving their greatest prestige under Alexander the Great, and regarded as the first or
Alexander Mosaic, showing the Battle of Issus, from the House of the Faun, Pompeii
A heavy cavalryman of Alexander the Great's army, possibly a Thessalian, though the Companion cavalry would have been almost identical (the shape of the cloak of the latter was more rounded). He wears a cuirass (probably a linothorax) and a Boeotian helmet, and is equipped with a scabbarded xiphos straight-bladed sword. Alexander Sarcophagus.
The Companions of Alexander the Great
Somatophylakes were the bodyguards of high-ranking people in ancient Greece.
Companion cavalry
…Great, and regarded as the first or among the first shock cavalry used in Europe. Chosen Companions, or Hetairoi, formed the elite guard of the king (Somatophylakes). The name of the military unit derives from Greek Hetairoi, those near the king. The Hetairoi (Companions) could be members of the Macedonian aristocracy…
Coin of Balacrus, somatophylax of Alexander the Great, as satrap of Cilicia, with letter "B" next to the shield, standing for B[AΛAKPOI]. Tarsos. 333–323 BC.