Osbeorn Bulax's father governed on what king's behalf?
Osbeorn Bulax Osbeorn (died c. 1054), given the nickname Bulax, was the son of Siward, Earl of Northumbria (died 1055). He is one of two known sons — probably the older — of Siward. While it is normally assumed he was the son of Siward's Bamburgh wife Ælfflæd, it has been suggested by William Kapelle that Osbeorn's mother was not Ælfflæd. The nickname "Bulax" probably represents the Old Norse term for "Poleaxe".
Rögnvald Brusason Rognvald was taken by his father to Norway, to the court of Olaf Haraldsson, when Brusi and Thorfinn went there to have the inheritance of Einar Wry-mouth's third-share of the Earldom settled. Olaf kept Einar's share for himself, appointing Brusi to administer it, and kept Rognvald at his court.