In Greek mythology, Epimetheus is Pandora’s brother-in-law because he is the brother of Prometheus. The two figures are Titans, and their contrasting names are often interpreted as contrasting kinds of thought: Prometheus is associated with foresight, while Epimetheus is associated with afterthought.
Zeus sends Pandora to Epimetheus, who accepts her despite Prometheus’s warning not to receive gifts from Zeus. Pandora later becomes Epimetheus’s wife in the standard version of the story. Their relationship places the container episode within the conflict between Zeus, Prometheus, and humankind.
Epimetheus is not the same person as Deucalion. Deucalion is Prometheus’s son and later becomes Pyrrha’s husband. Pyrrha, in turn, is commonly identified as the daughter of Pandora and Epimetheus.
The name Epimetheus helps explain his mythological characterization: he acts after events have unfolded. Modern retellings sometimes reduce him to a passive recipient, but his family connection and decision to accept Pandora are important parts of the ancient narrative.