Tostig Godwinson
Waltheof was the second son of Siward, Earl of Northumbria. His mother was Aelfflaed, daughter of Ealdred, Earl of Bernicia, son of Uhtred, Earl of Northumbria. In 1054, Waltheof's brother, Osbearn, who was much older than he, was killed in battle, making Waltheof his father's heir. Siward himself died in 1055, and Waltheof being far too young to succeed as Earl of Northumbria, King Edward appointed Tostig Godwinson to the earldom.