Greek Gods/Goddesses  Hestia and Poseidon.
Poseidon.
Background
Poseion's father was Cronos and his mother was Rhea. Poseidon is one of the three major gods in Olympus.  Zues and Hades, his brothers, are the other two.  Poseidon had gotten the sea, Zues, who defeated Cronos, got the sky, and Hades got the underworld.  
Poseidon rules more than just the sea.  He is the earthshaker, god of storms and a horse lover, since he himself created them.  Many sailors and traders, which most Greek citizens were back then, prayed to Poseidon for a safe sea voyage.  So, this God was NOT one to be angered. 

More on the God of the Sea

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1 god, 3 names
Poseidon was called Neptune in Rome.  He was called Nethuns in Etruscan.  No matter what they call him, he's still the same god.  Poseidon came "first", so the other gods are "copies", although Nethuns is a copy of Neptune.
Symbol and Powers
Every god has a symbol.  Poseidon's symbol was the trident and his sacred animals were the dolphin and the horse.  His trident was considered so powerful, that it was the cause of his earth shaking powers.  He could bring destruction to a place, but then restore peace to the area. 

Homes
Poseidon possessed two palaces, the one was up in Mount Olympus and the other was located at the bottom of the ocean and was decorated with jems and gold. Usually Poseidon preferred to stay with his wife, Amphitrite, at his underwater palace.
Appearance and personality.
Poseidon was said to be strong with long, blue hair.  Poseidon was considered to be the bad-tempered, moody and greedy god.  He would revenge himself when insulted, like he did to Odysseus, blinded his son, the cyclopes Polyphemus.  
Fun facts on Poseidon
1.  His wife was Amphitrite, a nymph and ancient sea-goddess, daughter of Nereus and Doris. 

2.  He was the father of many heros and mythical beasts. 
3.  He is also said to be the father of the hero Theseus (Mother: Aethra, queen of Athens) and the mythical horse Pegasus (Mother:  Medusa!).
4.  In order to keep Poseidons' temper down, people would drown their horses as a sacrifice to him.
5.  In addition to creating horses, he also created the Zebra.
6.  Poseidon and  Athena were in a competition to be the patron god for an Acropolis. It was decided that the god who created the most useful object would win the right to have the city named for them.  Athena created the olive, much more inmportant to the people of Athens than horses, so the name of the city-state became Athens.