(Ἀχαιός), according to nearly all traditions a son of Xuthus and Creusa, and consequently a brother of Ion and grandson of Hellen. The Achaeans regarded him as the author of their race, and derived from him their own name as well as that of Achaia, which was formerly called Aegialus. When his uncle Aeolus in Thessaly, whence he himself had come to Peloponnesus, died, he went thither and made himself master of Phthiotis, which now also received from him the name of Achaia. (Paus. 7.1.2; Strab. viii. p.383; Apollod. 1.7.3.) Servius (Serv. ad Aen. 1.242) alone calls Achaeus a son of Jupiter and Pithia, which is probably miswritten for Phthia.
[L.S]A Dictionary of Greek and Roman biography and mythology
Smith, William
A Dictionary of Greek and Roman biography and mythology. William Smith, LLD, ed. 1890