In Greek mythology, Pandora’s brother-in-law who warned Epimetheus was Prometheus.
Prometheus and Epimetheus are brothers in the mythic family of Titans. Prometheus is known for foresight and for helping humanity, while Epimetheus is associated with thinking after an event. When Zeus sends Pandora, Prometheus warns his brother not to accept gifts from Zeus.
Epimetheus ignores that warning and accepts Pandora. Their relationship is therefore central to the story’s setup: Prometheus recognizes the danger, but Epimetheus acts despite the advice. Pandora later opens the vessel containing the troubles that spread through the human world.
The warning is especially meaningful because the brothers’ names contrast their ways of thinking. Prometheus suggests forethought, whereas Epimetheus suggests afterthought. This contrast is a recurring interpretive feature of the myth, although modern retellings sometimes omit the warning entirely.