Bilhah was a handmaid of Rachel. When Rachel supposedly could not conceive children of her own, she gave her handmaid Bilhah to the prophet Jacob to bear children on Rachel's behalf, resulting in the births of Dan and Naphtali.
She and Jacob's eldest son Reuben had an adulterous affair with each other, and Jacob discovered it. As a result, Jacob prophesied that Reuben and his descendants would not be as fruitful as they should have been.
Reuben, you are my firstborn;
My might, the beginning of my strength and vigor,
Preeminent in dignity and preeminent in power [that should have been your birthright].
But unstable and reckless and boiling over like water [in sinful lust], you shall not excel or have the preeminence [of the firstborn],
Because you went up to your father's bed [with Bilhah];
You defiled it—he went up to my couch.— Genesis 49:3–49:4 (AMP)
Bilhah is the mother of Dan and Naphtali; thus, she is the progenitor of the Israelite tribes that correspond to those names.
Feminist author Margaret Atwood would use the natalist story of Rachel and Leah their handmaids Bilhah and Zilpah as the basis of the fictional dystopian, zealous Christian society featured in the anti-patriarchy novella The Handmaid's Tale.