Short answers, pulled from the story.
Poseidon is one of the twelve Olympian gods of ancient Greek religion, presiding over the sea, storms, earthquakes, and horses. He was the protector of seafarers and the guardian of many Greek cities and colonies. His Roman equivalent is Neptune.
The earliest written form of the name appears in Linear B script as Po-se-da-wo-ne, found on Bronze Age clay tablets from Pylos and Knossos. The origins of the name are disputed among scholars. One theory reads it as "lord of the earth" from elements meaning husband or lord and earth; another interprets the second element as related to a Proto-Indo-European root for water, making Poseidon a master of waters.
According to Homer and Apollodorus, after the Olympians overthrew the Titans, the world was divided by lot among the three sons of Cronus: Zeus received the sky, Hades the underworld, and Poseidon the sea. Scholars believe that in his earliest Bronze Age form Poseidon was an inland god of waters and earthquakes who became associated with the sea when Achaean colonists migrated to Ionia in the 11th century BC.
Poseidon punished Odysseus because the Greek hero blinded Polyphemus, the Cyclops who was Poseidon's son. Poseidon afflicted Odysseus with storms, caused the complete loss of his ship, killed many of his companions, and delayed his return home to Ithaca by ten years.
Poseidon was regarded as the tamer and father of horses, and in the oldest Arcadian and Boeotian myths he appears in the form of a stallion. He was credited with creating the first horse, called Skyphios, by striking a rock with his trident. He fathered the mythical horse Arion and, according to Hesiod, the winged horse Pegasus through the Gorgon Medusa. In Arcadia he was worshipped under the epithet Hippios, meaning "of the horse."
Major temples to Poseidon were built at Sounion in Attica, where the second temple dates to 444 BC; at Isthmia near Corinth, where a pioneering Doric structure was built around 690-650 BC; at Kalaureia, probably in the mid-6th century BC; at Taranto and Paestum in Italy; and at Tinos in the Cyclades, built in the 4th century BC of local marble and decorated with dolphins and tridents.