The hypaspists were the elite infantry unit in the army of both Philip II and Alexander III. In translations of the ancient sources they are often referred to as the "guards".
When Alexander crossed to Asia in 334 BC he had with him three battalions of hypaspists, each of 1,000 men. Their overall commander was Nicanor, son of Parmenion. Nicanor died (of natural causes) in 330 BC; at some point after his death Alexander appointed as their new commander Seleucus, who later became satrap of Babylonia, and then king of much of the eastern empire.
There is some debate about the arms and armour that the hypaspists carried; however, as the campaign went on Alexander re-fitted most of his troops, and the hypaspists adapted well to the guerrilla warfare required in Bactria and Sogdia between 329 and 327 BC.