Pandora's Box was a box on Earth Prime in the shape of a skull. Despite being found on Earth Prime, the box did not originate there, but rather from a different universe or dimension completely. Although credited for unleashing evil on Earth Prime, this was not the case as evil was present before the arrival of the box. The rise of the Seven Deadly Sins due to the box, however, did influence the impact evil had on Earth Prime, though.
A Mother Box in the shape of a three-eyed skull on Earth 3, the Pandora's Box was designed for two things. The first was to be a global bomb, which when connected to a being of great magical energy would temporarily connect all magical beings across the Multiverse. The second was to act as a gateway to and fro Earth 3.
After arriving on Earth Prime, the box of mysterious origin was fearful to only the most powerful beings at the time, the rulers of Earth Prime, the Olympian Gods. Fearful of what it could bring to Earth, they refused to approach it, instead coercing Pandora, from an early human tribe in Greece, to open it for them. She unleashed the Seven Deadly Sins, who called her mother, who proceeded to infect the evil in the world even more than before. The box was in truth a bomb, set to blow if one of the Wizard's champions touched it.
For most of history afterwards, the location of the box was unknown, though it was found in the nation of Gamora. Afterwards it was housed in the Black Room where it was stolen by Pandora. The search for the box later resulted in the Trinity War.