Acusilaus, Achelous was the "oldest and most honoured" of the river-god offspring of Oceanus. Servius, relating a tradition of unknown origin, reports that Achelous was said to have been the son of Earth (i.e. Gaia).

Achelous had various offspring. He was said to be the father of the Sirens. According to the 3rd-century BC poet Lycophron, the Sirens were the daughters of