Pandora's Pithos

 Pandora's Pithos (πίθος) (also known as Pandora's Jar/Box) was once the "home" to all the evils of the world. When Pandora, overcome by curiosity, opened it, they all escaped and made life worse for humans. It is often called Pandora's box. It is currently owned by Hestia and only the spirit of Hope (Elpis) remains in the Pithos.

History
Pandora's Pithos was given to Pandora by the gods. It was really a punishment to Prometheus for taking fire from the gods, and they knew he would get angry if he saw his creations be tormented, so they gave her the jar and told her not to open it no matter what. Percy remarked in The Last Olympian that Pandora must have been "totally ADHD" like him and the curiosity was killing her. When Pandora did open the jar and everything evil that mankind is tormented by, like lies, murder, treason, and all bad spirits and ideas escaped from that jar. The first Empousa was also released. Only Hope (Elpis) remained.

The Last Olympian
When Prometheus met with Percy, he gave Percy the jar. At the time, only Hope was left in the jar. He told Percy that when he was ready to surrender to Kronos, that he should open it, giving up hope. Although Percy put it in the hotel's safe, it followed him around, and appeared whenever he was at his weakest, tempting him to open it. Percy later gave it to Hestia as "hope survives best at the hearth".

Trivia

 * Most mortals call it a jar/box, rather than a Pithos, an Ancient Greek storage jar.
 * Prometheus is clueless as how the word box/jar came about, but admits that "Pandora's pithos" just doesn't have the same ring to it.