In Greek Mythology growing up, Kratos was a Spartan, serving his army of Spartans, though, when he leads his army to fight an army of Barbarians, the Spartans get picked off one by one. When Kratos is about to lose his life, he calls for Ares, the God of War, to give Kratos power, and he will be a servant of Ares. Ares accepts, and gives Kratos the Blades of Chaos, a formidable weapon to slay your enemies, letting him kill all the Barbarians.
Though, this all goes wrong, when Ares orders him to raid a village that Kratos' wife and daughter are. Kratos not knowing this, destroys the village, along with killing his wife and daughter. The only survivor of the village, The Oracle, cursed Kratos, forcing him to forever wear the ashes of his dead family on his skin, giving him pale white skin and being nicknamed: "The Ghost of Sparta." That day forward, Kratos wanted nothing but revenge on Ares.
For a few years, he serves the gods of Olympus so he can be forgiven for serving Ares, and have rid the memories of his pain. While on one of his missions, he had learnt that in order to kill Ares, he must open Pandora's Box to obtain the power to kill a god. Kratos goes inside Pandora's Temple and completes the trials to earn the Box. Soon enough, Ares knows of this, and steals the box. But soon enough, Kratos gets it back and gets his revenge by doing the impossible... killing Ares, A mortal killing a god. After Ares had fallen, Athena had told Kratos that the gods had forgiven him, but could not let him lose the memories of his past, for no man, no god, could ever forget the terrible things he had done. Feeling betrayed, Kratos falls off the highest peak in Mount Olympus, thinking death was his only escape from his torture... But his fate was not sealed. Kratos was pulled up from the sea, and back to land, with Athena at his presence. Athena tells Kratos that the gods do not want him dead, for there is now an empty throne for a new God of War. Kratos takes the throne and becomes the God of War.
Kratos had been the God of War for a while now, and with his new abilities, he helps his Spartan army raid areas. When the Spartans call for Kratos when in the middle of a war, Kratos emerges from his throne and gets ready. Athena tries to stop him, for the gods grew weary of his destructive behaviour, But Kratos brushes her off and jumps into battle. But then an eagle drops in and drains most of Kratos' God Powers, and the eagle uses it to bring a giant statue to life and attacks Kratos, but when Kratos destroys the statue, he is weakened, and then the Eagle comes down and is revealed to be Zeus.
Zeus informed Kratos that he didn't want to suffer the same fate as Ares, and demanded that Kratos surrender and serve him forever. However, when Kratos refused, Zeus attacked and killed him by driving the Blade of Olympus into his stomach. In his dying breath, Kratos swore that Zeus would pay for his betrayal. Kratos was dragged down by the arms of the Underworld. The Titan Gaia, who had been watching him his entire life, saved Kratos, sealed his wound, and gave him the strength to escape death. Climbing out from the Underworld, he went back in time to confront Zeus again. The fight ends with Kratos ready to drive the Blade of Olympus into his stomach, the same way he killed Kratos. Kratos charges to kill Zeus, only for Athena to jump in the way and take the blow herself. A distraught Kratos asked Athena why she sacrificed herself, to which she replied: "to save Olympus". She further revealed to Kratos that Zeus is his father and that his actions were driven by fear. Zeus' intention was to finally break the cycle of patricide by killing Kratos, whom he now recognized as the "Marked Warrior" destined to bring about the final destruction of Olympus.
Athena disappears into green dust, and so Kratos promises the destruction of Olympus. Kratos goes back in time to recruit the Titans before they got defeated in the Titan war years ago, and take them to the present era to finally exact his revenge on all of Olympus.
Kratos wants revenge. Revenge on all of Olympus, and he plans to do this by killing all the gods of Olympus. An injured Zeus orders Poseidon, God of the sea, to take down Kratos and the Titans. This is no challenge to Kratos, though, he easily kills Poseidon by gouging his eyes out and snapping his neck. With Poseidon's death, the seas unleashed a cataclysmic flood that engulfed all of Greece, drowning almost all of the Greeks, save for those on Olympia and other mountaintop locations. Gaia ends up betraying Kratos by letting him fall to his death. Kratos obviously survives, then goes on a god-killing Spree, kills multiple gods and takes their weapons. Hades' death caused all of the souls in the Underworld to run rampant, Helios' death caused the sun to be permanently veiled by dark clouds and rain storms. Hermes' death caused a deadly plague to spread across the land, affecting all human, animal, and plant life. Many others suffered by Kratos... When going for Pandora's box to kill Zeus, he realised he would need Pandora herself to put out the flame. Kratos brings Pandora to the box so she can sacrifice herself to put out the flame, Kratos has second thoughts, but Pandora says this is the only way, but the both are then confronted by Zeus. Kratos and Zeus battle, but then Pandora puts out the flame, killing her.
When the dust settles, Kratos opens the box, revealed to be empty, Zeus laughs, as he says this is another one of Kratos' failures. Gaia then returns to kill both Kratos and Zeus, so they jump into her chest area with her heart, where Kratos and Zeus start to finish the fight. Kratos stabs both Zeus and Gaia's heart, killing both. When Kratos thinks this is over, the spirit of Zeus emerges and kills Kratos and sends him into a world of Fear, where Kratos is shown all of the terrible things he has done in the past. Kratos escapes the world and back to reality with the power of Hope. He uses this to finally kill Zeus, ending Olympus. The spirit of Athena tells Kratos that the power of Hope was in Pandora's box, and that Kratos should give the power to Athena for Olympus. Kratos, having nothing to live for, takes the Blade of Olympus, and stabs himself with it, freeing the power of Hope. Athena, disappointed, rips the blade out of Kratos, killing him.
Though hours later, the body of Kratos is gone, and only a trail of blood is seen, ending at the Ocean.