Based on the formulaic nature of his ties to his predecessors, his strong affiliation with Agder, and the failure of an early saga dedicated to him to name any family connections, some scholars have suggested that the linkage to the earlier Yngling dynasty of Vestfold was a later invention, created to associate a conquering Halfdan and his son Harald Fairhair with the family glorified in the Ynglingatal, whom he had displaced.

To secure his claim to Raumarike, Halfdan first defeated and killed the previous ruler, Sigtryg Eysteinsson, in battle.

Fagrskinna and Heimskringla both agree that Halfdan's first wife was Ragnhild, daughter of King Harald Gulskeg (Goldbeard) of Sogn.

According to Heimskringla, Halfdan's second wife, also named Ragnhild, had been kidnapped from her home by Hake, a "berserker" who encountered her father in Hadeland and killed him.

)[3] Heimskringla, Fagrskinna, Ágrip and Historia Norwegiæ all relate that Halfdan drowned when he fell through the ice at the inlet Røykenvik in the lake Randsfjorden on his return home from Hadeland.

His horse and sleigh broke through ice weakened by cattle dung near a watering hole dug in the frozen lake.

[5][6] No contemporary sources mention Halfdan, and the details of his life that are provided by later kings' sagas are considered semi-legendary by modern historians.

Although he has his own saga in Heimskringla, it lacks any skaldic verse, which is normally used by Snorri as supporting evidence and this, combined with its rather legendary character, leads historians to be wary of seeing much veracity in it.