In Greek mythology, Achelous was originally the god of all water,and the rivers of the world were viewed by many as his sinews. Later, in Hellenistic times, he was specifically a river god who became the patron deity of the Achelous River, which is the largest river of Greece, and thus the chief of all river deities, every river having its own river spirit (though the initiated still revered him as the god of all water.
Achelous was also an important deity in Etruscan mythology,intimately related to water as in the Greek tradition but also carrying significant chthonic associations. Man-faced bull iconography was first adapted to represent Achelous by the Etruscans in the 8th century BC, and the Greeks later copied this tradition. Wiki