Poseidon is the god of the sea. He always carried a trident. When he was angry he would hit the water with it and it would cause terrible earthquakes, storms, and drownings.
Poseidon had a brother named Zeus. Zeus is the ruler of the sky. He was god of the sky, clouds, and rain. Zeus would carry around a lightning bolt.
Poseidon lived somewhere under the sea. There is a myth that Poseidon got when the Greeks lost a war. The soldiers tried to return to Greece on ships. Poseidon sent a huge storm over the ocean and it wrecked all of the ships. Sailors always thanked Poseidon when the seas were calm.