Cronus the Titan & his sister Rhea had 6 children: Zeus, Hestia, Poseidon, Demeter, Hades & Hera. Zeus divided the kingdom with his brothers. Zeus took Olympus & the heavens & Poseidon's cut was the Earth's seas & oceans.
Poseidon wanted a bigger piece of the pie & was always involved in negotiations with Zeus over land. He never got his way completely & usually had to settle for part of what he wanted.
The nereid Amphirite was Poseidon's wife & she was the daughter of the Titan Oceanus. Poseidon rode in a chariot pulled by Tritans blowing conch horns. Tridents, bulls & horses were his symbols. He had the power to call monsters up out of the ocean depths to avenge himself of humans & did just that in several instances.
In reference to his power to create earthquakes, he also called himself Earth-Shaker. He was an independant & turbulent god & he used his trident to stir the seas into awesome storms. Because earthquakes were part of Mediterranean life, Poseidon was honored with special festivals.