He is the second son of the Titans Cronus and Rhea, and brother of Zeus, Hades, Hera, Demeter, and Hestia.
Consorts & Children:
By his wife, the sea-goddess Amphitrite, he's the father of Triton, a merman, though he's also said to have fathered the mythical Pegasus (by Medusa), the cyclops Polyphemus, the legendary hunter Orion, and Theseus, the hero who defeated the Minotaur.
He is often depicted holding a trident, and riding a chariot drawn by hippocampi, or sea-horses. His sacred animals are horses, fishes, and dolphins.
Poseidon Around the World:
His Roman counterpart is Neptune, though he also has a Norse equivalent in Njordr.
SOURCES: Greek Mythology.com, MythWeb, Encyclopedia Mythica, & Wikipedia