Oannes

Oannes was a figure who introduced the civilized arts to modern man, including agriculture, written language, architecture, and mathematics. Once thought to be based on the ancient Babylonian god Ea, it is now believed that Oannes is in fact based on Adapa, the first of the seven antediluvian sages sent by Ea.

The following is a quote about Oannes by Berossus, a 3rd-Century B.C. Babylonian priest, taken from http://oannes.com/:

A man, or rather a monster, half man and half fish, coming from the sea, appeared near Babylon; he had two heads; one, which was the highest, resembled that of man, the other that of a fish. He had the feet of a man, and the tail of a fish; and his speech and voice resembled that of a man: a representation of him is still preserved. This monster dwelt by day with men, but took no food; he gave them knowledge of letters, arts, and sciences; he taught them to build towers and temples; and to establish laws; he instructed them in the principles of geometry; taught them to sow, and to gather the fruits of the earth; in short, whatever could contribute to polish and civilize their manners. At sun set he retired to the sea, in which he passed the night. There appeared likewise others of the same species.