Poseidon is the god of the sea in Greek mythology. He is one of the Twelve Olympian deities, often depicted with a trident, which symbolizes his power over the oceans, storms, and earthquakes. As the brother of Zeus and Hades, Poseidon held significant importance among the gods. His temperament could be volatile, leading to both calm seas and fierce storms, which reflected his dual nature. Poseidon is also associated with horses, reflecting ancient Greece's reliance on the sea for transportation, trade, and sustenance. His myths and stories emphasize the reverence and fear ancient Greeks had for the ocean's vast and unpredictable nature.