Zilpah was a handmaid of Leah. Leah and her sister Rachel were both married to the prophet Jacob. When Rachel supposedly could not conceive children of her own, she gave her handmaid Bilhah to Jacob to bear children on Rachel's behalf, resulting in the birth of two sons. Leah then copied Rachel's strategy and had Jacob take Zilpah as an additional wife as well, resulting in the births of Gad and Asher.
Zilpah is the mother of Gad and Asher; thus, she is the progenitor of the Israelite tribes that correspond to those names.
Feminist author Margaret Atwood would use the natalist story of Leah and Rachel their handmaids Zilpah and Bilhah as the basis of the fictional dystopian, zealous Christian society featured in the anti-patriarchy novella The Handmaid's Tale.