Valerica is a Nord vampire lord and member/former member of the Volkihar vampire clan. She is the mother of Serana and has an estranged husband named Lord Harkon.
Valerica and her daughter took part in the vile ritual demanded by Molag Bal to become vampire lords. She became estranged to Lord Harkon after he became abscessed with a prophecy to block out the sun and was willing to sacrifice his daughter in order to do so seeing it as a benefit to all vampire kind. Valerica then sealed Serana away (without telling her why) to keep her from her father.