Poseidon is the god of the sea in Greek mythology. He is the older brother of both Zeus and Hades and second oldest of his siblings behind Hestia. Poseidon functioned as an antagonist of other gods usually not through direct malevolence but rather as a result of egotism and uncontrollable fits of anger; he is also the major antagonist in the epic poems of The Iliad and The Odyssey as well as in Mission Odyssey.
At the begining of the serie, he make a bet with Athena : he told her that he will never be able to reach his homeland Ithaca.
After the victory of Odysseus over the Trojan, the Odyssey continues following the voyage of Odysseus as he was taken to the island of a Cyclops who were some of Poseidon’s sons. Not knowing what dwelt on the island and being quite lost Odysseus and his men docked to ask for directions and replenish their supplies. They encountered one of Poseidon’s sons named Polyphemus. Polyphemus captured Odysseus and several of his men in his cave and refused to open it until the morning when he ate them. Odysseus lulled Polyphemus to sleep by encouraging him to have the wine he had bough for bartering and when he was asleep stabbed him in the eye with an arrow, the confused and enraged cyclops fumbled around trying to find Odysseus but could not so he opened the door and waited for them to try to pass him, but Odysseus had already counted on this and covered himself and his men in sheep skins, bleating as they passed by with the rest of Polyphemus' heard of sheep so he could not tell them apart. As Odysseus escaped the isle Polyphemus called out to his father to avenge him and so Poseidon’s anger at Odysseus became a full-out campaign of torment to see that he never saw the shores of Ithaca again as he sent him from one strange and dangerous uncharted island to another.
He allies himself with Charybdis and Scylla, mermaids, Circe, the Gorgons Medusa and Stheno, Harpies, the God Aeolus, Centaurs, Amazons, lotus-eaters, Lycaon the king of Arcadie, Nausicaa, Naiads and many others.However, after the events with Cronus where he is captured by his fathers in the Tartarus and is rescued by Odysseus, he concents to helps Odysseus and his friends to escape the Tartarus but keep his grief against him