Throughout the series, Kratos is portrayed as an anti-hero, often performing questionable actions.
An oracle foretold that the demise of Olympus would come not by the revenge of the great Titans, imprisoned after the Great War, but by a marked warrior. The Olympians Zeus and Ares believed this warrior to be Deimos, the brother of Kratos, due to his strange birthmarks. Ares interrupts the childhood training of Kratos and Deimos in Sparta (with Athena watching) and kidnaps Deimos. Kratos attempts to stop Ares, but is swept aside and scarred (across his right eye) by the Olympian. Taken to Death's Domain, Deimos is imprisoned and tortured for many years by the god of death, Thanatos. Believing Deimos to be dead, Kratos marks himself with a red tattoo (identical to his brother's birthmark) to honor his sibling.
Kratos eventually becomes the youngest Captain of Sparta's army, but is revealed to have had a thirst for power. Faced with total defeat at the hands of a barbarian horde, Kratos called for aid to Olympian god Ares. Given the Blades of Chaos, Kratos destroys his enemies and blindly follows the God of War, killing hundreds in his name. After Ares tricks Kratos into murdering his wife Lysandra and daughter Calliope in a temple dedicated to Athena, the Spartan is shocked out of his bloodlust and renounces service to Ares. As the temple burns, a village oracle curses Kratos and condemns him to wear the "mark of his terrible deed", being the ashes of his family. The ashes turn Kratos' skin ash-white, earning him the title "Ghost of Sparta."
Although Kratos then vows to serve the other gods in order to receive forgiveness and relief from the nightmares of his past deeds, he is openly defiant. Kratos is reluctant to aid the gods when Helios is kidnapped, and openly abandons them when the goddess Persephone offers him a chance to be reunited with his daughter. Kratos, however, is eventually forced to reverse his decision when Persephone uses the Titan Atlas in a bid to destroy the world and in turn Calliope. Knowing that while intervention will save Calliope it will keep them apart forever, a bitter Kratos kills Persephone, imprisons Atlas and frees Helios (Chains of Olympus).
When Kratos grows tired of his service and confronts patron Athena, the goddess advises that if Kratos will kill the rampaging Ares, the gods will forgive his sins. Kratos once again agrees out of selfish motives, and after finding and using Pandora's Box, is ultimately successful. Despite being free of Ares' influence (including the Blades of Chaos), Kratos is not relieved of the nightmares that haunt him: only forgiven. A dissatisfied and despairing Kratos attempts to commit suicide, but is saved by Athena, who guides Kratos to Olympus (giving him the Blades of Athena) where he becomes the new God of War (God of War).
Still haunted by the visions of his mortal past, Kratos - against the advice of Athena - embarks on a quest to find his mother, Callisto, in the city of Atlantis. Callisto attempts to reveal the identity of Kratos' father before being transformed against her will into a beast that Kratos is forced to kill. Before dying, Callisto advises Kratos to find his brother Deimos in Sparta. Kratos first frees the Titan Thera from imprisonment, which causes the destruction of Atlantis. After a skirmish with his brother Deimos, Kratos allies with his sibling to battle the God of Death Thanatos. Thanatos kills Deimos but is then killed in turn by Kratos, who returns to Olympus enraged at the gods (Ghost of Sparta).
Eventually shunned by the other gods and bored with life on Mt. Olympus, Kratos spends his time watching the Spartan army overrun Greece. After being falsely accused of committing murder and eventually killing Ceryx, the son of Hermes (Betrayal), Kratos joins the Spartan army in city of Rhodes, intent only on destruction. Zeus, however, weakens Kratos, and then tricks him into abandoning his godly powers into the Blade of Olympus (which Zeus uses to kill Kratos). Although Kratos overcomes all obstacles, he is stunned at Zeus' betrayal and swears revenge as he dies.
As Kratos falls into the Underworld, he is rescued by the Titan Gaia. Banished to Tartarus with the other surviving Titans after the First Great War, Gaia and her brethren seek the death of Zeus. Kratos, fuelled by anger at the betrayal, agrees to aid the Titans and is instructed to find the Sisters of Fate, with their power being capable of returning him to the moment of Zeus' treachery.
Kratos becomes both determined and utterly ruthless—in the pursuit of his goal he wounds a Titan, kills several Greek heroes without hesitation and deliberately sacrifices two scholars. All three of the Sisters of Fate are killed when they oppose Kratos, and in a final confrontation with Zeus is prepared to execute the King of the Gods. Zeus is only saved when Athena intervenes and sacrifices herself for him, with Kratos only then showing some remorse. Learning from a dying Athena that Zeus is in fact his father, and that Zeus wishes to avoid a repetition of what he himself did to his own father Cronos, Kratos rejects any notion of a relationship and vows to kill both Zeus and destroy Olympus. Encouraged by Gaia, Kratos uses the power of the Fates to retrieve the Titans prior to their defeat in the Great War, and with their aid, storms Mt. Olympus (God of War II).
Although Kratos kills Poseidon, he is abandoned by Gaia when an initial encounter with Zeus goes poorly. Stranded in the underworld and now betrayed by both the Olympians and Titans, Kratos learns from the spirit of Athena (who also provides the Blades of Exile) he will need to find the Flame of Olympus: the key to Zeus' defeat. Kratos murders both Titans and gods alike, ignoring the warnings of his victims as he seeks the Flame. Realizing the key to pacifying the Flame and reaching what is discovered to be Pandora's Box is in fact Pandora herself, Kratos comes to care for the girl, who reminds him of his lost daughter Calliope.
Kratos shows humanity when he attempts to stop Pandora from sacrificing herself to quenching the Flame, but reluctantly allows the act when Pandora states there is no other option. Finding the Box empty, and driven berserk by Zeus' mockery, Kratos attacks his father. Although Gaia intervenes and attempts to kill both Kratos and Zeus, she is destroyed by Kratos, who then apparently defeats Zeus.
Zeus, however, returns and attacks Kratos in spirit form. Kratos, now retreated into his psyche, comes to forgive himself for his past sins with the help of Lysandra. Pandora later appears and tells Kratos that hope will ultimately save him. A now whole Kratos is revived and easily destroys Zeus. Athena confronts Kratos and demands that Kratos return what she placed in Pandora's Box: hope. In a selfless act, Kratos refuses and impales himself on the Blade of Olympus, which disperses the power across the world for mankind's use. Athena departs as Kratos states that his need for vengeance is at an end.
Kratos' ultimate fate remains unknown (God of War III).