|“||Hope is what makes us strong. It is why we are here. It is what we fight with when all else is lost..||”|
Hope is a blessed power and the "most powerful weapon in the world" according to Athena, powerful enough to kill any god, even Zeus himself. It was originally possessed by Athena before she placed it into Pandora's Box to counteract the Evils, but later went to Kratos and then was freed to mankind by his sacrifice.
In the Legend of Pandora, Pandora simply could not resist the temptation of what was inside Pandora's Box. Curiously opening the box, she released all of the world's evils; pride, wrath, lies, anger, hate, despair, arrogance, envy, vanity, lust, fear, misery, greed, etc.
At the bottom however, underneath all the evils that poison/influence/corrupt the hearts, minds and souls of the humans, there was hope. It did not abandon humans and, as such, stayed with them.
In the God of War Series
Long ago, when Zeus sealed the evils of the Titanomachy within Pandora's Box, Athena feared that the box would one day be opened and release the dark forces that it held. As a safeguard, she placed Hope - a power great enough to kill a God - inside the Box with the myriad evils.
In God of War, it was believed that Kratos had absorbed the evils of Pandora's Box in order to defeat Ares. However, Kratos had actually consumed the power of Hope to gain the strength to defeat his former master. From the time of the end of God of War to the end of God of War III, Hope was trapped behind layers of guilt. Apart from unknowingly using it to slay the God of War, Kratos was not able to use Hope's power again until he had forgiven himself for his perceived sins.
After his fall from Mount Olympus during the beginning of the Second Titanomachy, Kratos encountered Athena's Spirit in the Underworld. She advised him to seek out Pandora's Box once more, in order to use the power of Hope that she believed it still contained against Zeus. During his quest, Kratos met the living key to the Box's protection, Pandora, who strongly believed that Hope was the core force that let the living keep on living. However, when Kratos managed to open the Box, it was completely empty.
Eventually, with the help of Pandora, Kratos managed to forgive himself while wandering throughout the fear and chaos of his soul and reawakened the long-dormant power of Hope. With the power of Hope, Kratos was able to defeat the spirit of Zeus and finally fulfilled the revenge that he had long sought.
Athena then appears and demanded that Kratos return to her the power of Hope. Kratos then stated that the Box was empty. She didn't believe him at first but Athena then realized that the power of Hope that she initially hid inside the Box actually was absorbed by Kratos during his final battle with Ares while all the evils infected the Olympians, which corrupted them. As Kratos refused to give Athena the power of Hope as he was tired of always being used as a pawn, he instead impaled himself with the Blade of Olympus, and thereby released the power, which granted Hope to humanity. Athena, after she said that Mortals could not yet wield such power, pulled out the Blade of Olympus from Kratos' torso and walked away. Kratos lain on the ground and dying, found solace in his actions, had finally forgiven himself for the murder of his family, and felt ready to let the Underworld take him.
But as the post-credits scene revealed, Kratos was no longer on the ground. In Kratos' stead, a trail of blood led back to the sea. It is revealed that he is cursed to forever walk the earth for his terrible sins, thus unable to die. Finding no reason to stay in Greece, he moves to Nordic lands. During this time with the power of Hope now given to humanity, the people of Greece have learned to move on and rebuild without the need of the Olympian Gods. As seen on the Amphora Vase within Tyr's Vault.