In Greek mythology, Achelous is the deity of the river of that name, and ruler of all rivers. He is the eldest son of Oceanus and Tethys. He fought with Heracles for Deianira, a Greek princess. Despite assuming many forms, among which that of a bull, Achelous was eventually vanquished. Heracles broke off one of his horns and nymphs fashioned it into the Cornucopia ("horn of plenty"). Achelous is usually depicted as a bull with the torso of a man and a bearded face (common for river gods, especially on coins), but also as an old, grey man with horns. (Ovid VIII, 547; IX, 1).
Achelous is the name of the largest river in Greece (in ancient times called Aspropotamos).