Pandora's Box is one of the 13 Artifacts. It is also known as Obsidian Stone and/or Odin's ring. It bonded with a woman named Alina Enstrom. The box once activated induces unbridled chaos in the hearts and minds of everyone within it's range. While attaching to Alina after she used both stone to open it, the box sent out waves of energy that cursed any and all sentient life to violently slaughter one another by controlling their emotions. As Balance of Ember Stone and Glacier Stone Pandora's Box also had the same effect on both of said wielders, forcing the two to fight one another even during their temporary cease fire.
The titan Prometheus stole fire and gave it to man, as punishment Zeus sent man Pandora, and then sent her a Urn. The urn contained the worlds evils and once Pandora opened it, all these evils were let lose on the world. Pandora closed the urn and trapped Hope inside.
After Zeus had given life to Pandora, he gave her a sealed chest to guard and told her not to open it (knowing full well she eventually would, making her a pawn in his grand plan). She opened it and thus released evil upon the world. Since then, she has been slaying demons with her dagger Hope, sending them back to the sealed chest.
DC - The New 52
Pandora's Box was opened by Pandora, releasing the tragedy, torment, torture and terrors of man. Subsequently, she was judged by the Wizards of the Rock of Eternity, and sentenced to an eternity of loneliness and pain for her crime. The Box was then found by a team which involved Steve Trevor of A.R.G.U.S., and led to the deaths of many soldiers who tried to contain it. The Box was stolen back by Pandora, and appears to be the focus of the Trinity War.
It has been revealed by The Outsider that Pandora's Box is a doorway to another universe that was originally created on Earth 3 and contrary to popular belief it's not magic but science. He also revealed it can only be opened by someone from Earth-3