Achelous

In Hesiodic tradition Achelous is counted among the potamoi as a son of the primordial Titans Oceanus and Tethys, placing him in the elemental generation of river deities. Other poetic and mythographic traditions vary his genealogy and emphasize his antiquity and prominence among rivers (accounts summarized across classical authors and later mythographers). He functions etiologically as the source or father of multiple springs and nymphs (e.g., Pirene, Castalia, Dirce, Callirrhoe) and in some traditions fathers the Sirens, showing his role as progenitor of local water-associated divinities.

Classical sources present Achelous as a frequent shapeshifter. In the Heracles episode he assumes a bull form; Sophocles (Women of Trachis) describes him alternating among three shapes: a bull, a coiled serpent, and 'ox-faced with human trunk,' the latter passage adding the image of fountain-water spraying from his beard. Later poetic treatments emphasize bull and serpentine imagery and hybrid man–bull features; one horn of his bull-form is broken off in the Heracles narrative and subsequently becomes associated with the cornucopia motif in Ovid and Hyginus.

Achelous is portrayed as a powerful river-force and a metamorph who can change shape (bull, serpent, hybrid). Mythic narratives attribute to him paternity of naiads, springs, and in several accounts the Sirens; poets and mythographers link him to specific springs (Pirene, Castalia, Dirce, Callirrhoe). The breaking of his horn by Heracles and its transformation into a horn of plenty (cornucopia) in later authors underlines his symbolic role as a source of abundance. Ancient rationalizing authors (Diodorus, Strabo as reported in summaries) present Heracles' contest with Achelous as an etiological account for diverting or confining a river—these are narrative explanations of human alteration of a river's course rather than described supernatural limitations intrinsic to the deity.