Poseidon: the sea god who drowned Greece

Poseidon was the Olympian God of the Seas, Rivers, Storms, Earthquakes, and Horses, a son of the Titans Cronos and Rhea and brother to Zeus and Hades. His domain made him among the mightiest of the pantheon, his power considered second only to that of Zeus. Though he aided Kratos in the Spartan's early quests, the destruction Kratos brought to his domain turned the King of the Oceans against him, and Poseidon fell defending Olympus in the Second Titanomachy. (God of War (2005); God of War III)

How did Poseidon die in God of War?#

Kratos and Gaia knocked him out of the giant water form he fought in at the start of the Second Titanomachy, and Kratos beat him, gouged out his eyes and broke his neck, loosing a flood that drowned most of Greece. (God of War III)

The First Titanomachy#

When it was prophesied that Cronos would be overthrown by one of his children, the Titan King swallowed his offspring to prevent it, and Poseidon, like most of his siblings, spent a long imprisonment within his father's belly until Zeus freed them. Seeking retribution, Poseidon joined the rebellion against the Titans and helped decide the Great War. (God of War II; Theogony)

In the novelization of God of War II, he is said to have challenged the ancient Titan Oceanus over supremacy of the seas, summoning all the water in the world to overthrow him. During the final battle he aided his brother Hades against the mighty Atlas, general of the Titans: when Atlas saved Cronos from having his soul taken, Poseidon's lightning brought the Titan to his knees, allowing Hades to seize his soul. After Zeus forged the Blade of Olympus and banished the Titans to Tartarus, Poseidon was given dominion over all the seas. He took the Oceanid Amphitrite as his wife and ruled the waters of Greece, honored by mortals and immortals alike for safe passage. (God of War II; God of War II (novel); Theogony)

Aiding the Ghost of Sparta#

When the Hydra, summoned by Ares, terrorized the Aegean Sea, Zeus's edict against the Gods intervening directly against one another meant Poseidon could not strike the beast himself. In the novelization of God of War, Athena gained an audience at Zeus's behest with the King of the Oceans and informed him of the Hydra rampaging through his domain. Enraged at Ares, Poseidon was calmed by Athena and agreed to aid Kratos, the war god's former servant. (God of War (2005); God of War (novel))

Amid the storm, a representation of Poseidon granted Kratos the gift of Poseidon's Rage, a power that cast lightning through his body into his enemies and proved decisive against the Hydra King. The novelization adds that when Ares learned of this aid, he confronted Poseidon on the shores of Egypt, the two as vast as Titans yet unseen by mortal eyes. Poseidon warned that any further incursion into his domain would be destroyed, though Ares eased the standoff by sowing doubt about Athena's motives. Poseidon was later honored with a section of Pandora's Temple, where Kratos claimed the Trident that let him breathe underwater, and his imprisoned daughters, the Nyads, were freed. (God of War (2005); God of War (novel))

The destruction of Atlantis#

After Kratos joined the Gods following Ares's death, visions of his mother drew him to Atlantis, one of Poseidon's sacred cities. Poseidon loosed Scylla, her brood, and his Tritons to stop the Spartan, but Kratos defeated Scylla and inadvertently freed the imprisoned fire Titaness Thera, whose release shattered the foundations of Atlantis and sank it into the ocean. (God of War: Ghost of Sparta)

Though he did not appear in person, Poseidon assailed Kratos with whirlpools and hazards and manifested through a shattered statue, vowing that he would never forget what Kratos had done and that the Spartan would one day answer for the loss of his beloved city. As the years passed, Poseidon grew increasingly suspicious of Zeus's behavior, secretly doubting his brother's ability to protect Olympus. (God of War: Ghost of Sparta; God of War III)

The Second Titanomachy and death#

When Kratos and the Titans assaulted Mount Olympus, Poseidon was among the Gods who answered Zeus's call to unite, setting aside his grievances. He held back at first, letting Hades, Helios, and Hermes engage the Titans, then dived from the mountain into the chest of the Titan Epimetheus, killing him almost instantly and dealing the first blow to the rebellion. Plunging into the waters below, he summoned tendrils and his Hippocampi to restrain Gaia while emerging within a colossal watery construct in his own image. (God of War III)

Poseidon proved more than a match for both Kratos and Gaia, but he underestimated their coordination, and together they knocked him from his monstrous water form. A bloodthirsty Kratos then beat the weakened God of the Seas into a pulp before gouging out his eyes and breaking his neck. Poseidon's death was a devastating blow to the Olympians, who lost one of their mightiest defenders at the war's outset, and a catastrophe for mortals: a cataclysmic flood surged from his demise and engulfed nearly the whole of the Greek world, drowning the overwhelming majority of its people. (God of War III)