Poseidon's symbol was the trident, which was also a weapon, resembling a three-pronged spear, with which he could control the ocean, summon storms and earthquakes, and destroy objects.
Sometimes the lord of the sea is depicted riding a chariot over water. Horses had a special significance for Poseidon. He was also referred as the god of horses, and it was he who created the first member of the species.
He was able to transform himself to different creatures. Especially in his domain, the oceans, he could take many forms - even that of sentient water.
He was the brother of Zeus and Hades and was second only to Zeus among the Olympian gods; however, he also resided in a giant palace under the sea, which he shared with his wife, the goddess Amphitrite and their son Triton.
With fluid shapeshifting as one of Poseidon's strengths, he often used that ability for adulterous purposes. This is a trait he shared with his brother, Zeus. Arguably, they may have even been competing with each other.
There was a degree of rivalry between the two brothers. Though Poseidon realizes Zeus is the king of gods and that his powers surpass that of the god of the seas, he only obliges when he has to. And when he has to he doesn't act rebelliously, but rather with submissive stance. However, such was the sea-god's pride that it makes him a conspirator in one instance, where he, Hera and Athena attempt to chain Zeus.
Like his brother Zeus, Poseidon had several affairs with mortal women and goddesses and bore a number of children to them; among his mortal offspring were Atlas (not to be confused with Atlas the Titan), who became the first king of Atlantis and Theseus, the hero who killed the Minotaur, whom he begat with Aethra, a beautiful Greek queen. There is also a long list of monstrous offspring of Poseidon ranging from different giants and cyclopes, one of whom was Polyphemus, a cyclops who was blinded by Odysseus leading to Poseidon delaying the hero's journey home; the winged horse Pegasus, who was born after he impregnated Medusa and sprang from his mother's blood; the golden fleeced ram Khrysomallos; and the Ichtyocentaurs.