Poseidon, the god of the sea, was the brother of Zeus. He shared many similarities with his brother, especially his appearance. Yet while Zeus sometimes displayed a playful and humorous side, Poseidon always seemed moody, morose, and even downright angry. Poseidon s prickly personality made him a god to be avoided, both by mortals and by other gods. Yet as ruler of the waters, Poseidon was an important deity for the Greeks, particularly since much of their life revolved around the sea. While it was a good idea to avoid Poseidon, it was also necessary to keep him happy.