Poseidon was the god of the sea, son of Kronos and Rhea. He became ruler of the sea when the universe was divided after the fall of the Titans. Poseidon was bad-tempered and when he became angry, he would cause earthquakes. He managed to upset even Hades, the ruler of the underworld. Poseidon was most often depicted with his trident, and sometimes riding a horse (he is sometimes claimed to be the creator of horses).