Achelous
Ἀχελῷος
God of Greece's greatest river, who lost a horn wrestling Heracles for a bride.
He is held to be the greatest river in Greece and the father of the Sirens.
He fought Heracles over Deianira, shifting shape from serpent to bull — and lost when his horn was torn off in bull form.
Ovid passes down a version in which nymphs filled that horn with fruit and flowers, making it the horn of plenty. The horn a river god lost became overflowing harvest — the bond between flooding rivers and fertile fields, written as myth.
SourcesOvid, Metamorphoses