In the Greek myth of Pandora, Zeus gives her a jar filled with evils.
In Hesiod’s Works and Days, Zeus directs Pandora’s creation and sends her to Epimetheus. The container associated with her is described as a large storage jar, called a pithos in Greek. Its contents represent destructive conditions that spread among humans after the jar is opened.
The myth belongs to a larger sequence involving Prometheus. After Prometheus deceives Zeus and steals fire for mortals, Zeus responds by preparing a punishment for humanity. Pandora becomes the human-facing part of that punishment, while Prometheus receives a separate individual punishment.
The common expression “Pandora’s box” arose because the Greek word pithos was translated into Latin as pyxis, a box. The original story therefore features a jar, although “Pandora’s box” is now the standard English phrase.