In Greek mythology, Achaeus or Achaios (; Ancient Greek: Ἀχαιός, romanized: Akhaiós, lit. 'griever'', derived from αχος achos, 'grief, pain, woe') was the name of three mythological characters:
Achaeus, son of Poseidon and the eponym of Achaea.
Achaeus, son of Xuthus and mythical founder of Achaean race.
Achaeus, son of Phthia, daughter of Phoroneus and the god Zeus.


