Elpis is the personified spirit (daimona) of hope and expectation. She is the mother of Pheme, the spirit of fame and rumor. At the dawn of humanity, Zeus trapped Elpis and many of her evil counterparts in a jar (pithos) and entrusted it to the care of Pandora, the first woman. When Pandora opened the jar against Zeus' orders, all of the spirits escaped except for Elpis, who remained behind to comfort mankind.
Elpis, the Spirit of Hope, would not abandon humanity. Hope does not leave without being given permission. She can only be released by a child of man.
–The Last Olympian
History and Myths
Elpis is the spirit of hope and was the only good thing placed in Pandora's pithos. When Pandora opened the jar and unleashed its evil contents onto the world, Elpis was the only remaining benevolent spirit, staying with humanity so they would not give up hope.
In The Last Olympian, when Prometheus was enlisted to organize a truce between the demigods and Titans for a peaceful end to the fighting, he had Pandora's pithos in his possession. When Percy Jackson refused, Prometheus gave him the jar so that when he was ready to surrender, all he had to do was release her, symbolically "giving up hope." Though Percy was tempted to throughout the entire battle, Elpis was never released. In the end, Percy gave her to the goddess Hestia for safekeeping, because "hope survives best at the hearth." Hestia has since retained guardianship of the pithos.
(Note: Although her essence is trapped within the jar, Elpis can temporarily project her consciousness outside of it, taking on a physical form to spread hope to and reproduce with mortals. There are several limitations to this ability, however: Elpis can only project to locations where hope is especially strong, and she can only maintain these projections for short amounts of time (think a week or less) before needing to return. At the end of her pregnancy, she must project outside of the jar once again to give birth.
While Elpis remains trapped inside the pithos, her ability to spread hope to the world is limited. She can only project her consciousness to places where hope is already strong, not to the places that need it most. Thus, it is worth the effort for Elpis to conceive more demigod children, who can spread hope around the world in her place. This also furthers her influence, so she will have more places where she will be able to travel via consciousness projection.)
Daimona of Hope and Expectation Goddess of Hope and Expectation Spirit of Hope