http://en.wikipedia.org/wiki/Osburga

Osburga or Osburh was the first wife of King Æthelwulf of Wessex and mother of Alfred the Great, "a religious woman, noble both by birth and by nature".

Osburga's existence is known only from Asser's Life of King Alfred. She is not named as witness to any charters, nor is her death reported in the Anglo-Saxon Chronicle. It is presumed, but nowhere recorded, that she was also the mother of Alfred's older brothers Æthelstan of Wessex, Æthelbald of Wessex, Æthelberht of Wessex, Æthelred of Wessex, and of his sister Æthelswith, wife of King Burgred of Mercia. The internal chronology of Asser's life suggests that Osburga was alive after the second marriage of Æthelwulf, to the Carolingian princess Judith, in 856.

Osburga is described as the daughter of Oslac, pincerna of Æthelwulf's royal household. Oslac is described as a descendant of the fictitious Jutish kings Stuf and Wihtgar, and is also ascribed Gothic ancestry. Asser may not however have been familiar with Bede,who writes that the Jutish inhabitants of the Isle of Wight- descendants of Stuf -were "destroyed", so it is unlikely that Oslac was their descendant. Oslac and Osburga are known to have held Arreton Manor on the Isle of Wight. Oslac is described as "The Chief Butler of England", although it is uncertain what this title implies. Asser clearly identifies "Gothic" as synonymous with "Jute", although this is also uncertain. Ironically Alfred's Jutish blood and descent from the Isle of Wight kings more likely came from his father's side, via the sister of King Arwald, wife of Egbert I of Kent