 He has also suggested that the legend of Harald Fairhair developed in the twelfth century to enable Norwegian kings, who were then promoting the idea of primogeniture over the older custom of agnatic succession, to claim that their ancestors had had a right to Norway by lineal descent from the country's supposed first king.In the Saga of Harald Fairhair in "Heimskringla", which is the most elaborate although not the oldest or most reliable source to the life of Harald, it is written that Harald succeeded, on the death of his father Halfdan the Black Gudrödarson, to the sovereignty of several small, and somewhat scattered kingdoms in Vestfold, which had come into his father's hands through conquest and inheritance.His protector-regent was his mother's brother Guthorm.