In Greek mythology, Prometheus is Pandora’s husband’s brother and the father of Deucalion.
Pandora’s husband is Epimetheus, and Prometheus is Epimetheus’s brother. Prometheus is famous for stealing fire from the gods and giving it to humanity, an act that provokes Zeus’s punishment. In the mythic sequence, Zeus sends Pandora to the human world after this theft.
Prometheus is also traditionally named as the father of Deucalion. Deucalion later becomes the husband of Pyrrha, who is often identified as Pandora and Epimetheus’s daughter. These relationships connect the jar story to the flood story that follows in Greek mythology.
Ancient genealogies can vary from one source to another, but the Prometheus–Deucalion relationship is a standard version. The question distinguishes Prometheus from Epimetheus: Prometheus is Pandora’s brother-in-law, not her husband.