Epeius was the son of Endymion who married Anaxirrhoë. There was also an Epeius who was the son of Panopeus and built the Trojan horse (with, of course, the help of Athena). The name means 'successor' (epion), and certainly Endymion's son won the race for the succession to the throne. The same word can also mean 'attacker', and this will do very well for the other Epeius.