"My suitor was the river Achelous,
who took three forms to ask me of my father:
a rambling bull once, then a writhing snake
of gleaming colors, then again a man
with ox-like face: and from his beard's dark shadows
stream upon stream of water tumbled down.
Such was my suitor"
~ Deianeira, Sophocles, The Trachinia
Achelous, god of fresh water, prince of all rivers, deity of the Achelous river, son of Gaia and Oceanus and father of the sirens. Often portrayed as a man-faced bull, sometimes with a serpent-like body. He is described as having long hair wreathed with reeds and has been depicted as both old and in his prime.
An important deity, invoked in prayers, sacrifices and oaths, Acheleous ran into trouble when Hercules became his rival for love.
Achelous sought to marry Deianira, daughter of the king of Calydon and famed beauty. But he wasn't the only suitor. To determine who would become Deianira's husband, The king held a contest of strength which attracted the attention of Hercules. During the match, Hercules broke off one of Archelous' horns (which later became the legendary cornucopia/horn of plenty) forcing him to surrender.
An ABCs of Gods, Myths, and Superstitions.