Halfdan the Black Godfreyson (died 864) was the father of the first King of Norway Harald I.
His father was King Godfrey The Noble Halfdanson of Haithabu.
The saga of Halfdan the Black appears in a number of places online (see External Links below). It tells the following story:
Halfdan's mother was named Asa. She was the daughter of King Harald of Agder. When Halfdan's father was killed, Asa took the year-old Halfdan and returned to Agder, where Halfdan grew up.
When he was eighteen years old (i.e., 22 years before his death at age 40 in 864), Halfdan became king of Agder. He quickly began adding to his kingdom through political negotiation and military conquest. He divided the kingdom of Vestfold with his brother Olaf and, through military action, persuaded King Gandalf of Vingulmark to cede half his kingdom.
Next, Halfdan subdued an area called Raumarike. To secure his claim to Raumarike, Halfdan first defeated and killed Sigtryg, the previous ruler, in battle, then defeated Sigtryg's brother and successor Eystein in a series of battles. This established Halfdan's claim not only to Raumarike, but also to half of Hedemark, Sigtryg and Eystein's core kingdom.
Halfdan first wife was Ragnhild, daughter of King Harald Gulskeg (Goldbeard) of Sogn. Halfdan and Ragnhild had a son named Harald after his grandfather, and they sent him to be raised in his grandfather's court. Harald Gulskeg, being elderly, named his grandson as his successor shortly before his death. Ragnhild died shortly after her father and the young king Harald fell sick and died the next spring. When he heard about his son's death, Halfdan traveled to Sogn and laid claim to the title of king. No resistance was offered and Halfdan added Sogn to his realm.
The sons of Gandalf of Vingulmark, Hysing, Helsing, and Hake, attempted to ambush Halfdan at night but he escaped into the forest. After raising an army, he returned and defeated the brothers, killing Hysing and Helsing. Hake fled from the country and Halfdan became king of all of Vingulmark.
Halfdan's second wife was also named Ragnhild. She was the daughter of Sigurd Hjort, king of Ringerike. She was kidnapped from her home by Hake, a berserker who encountered her father in Hedemark and killed him. In turn, Halfdan had her kidnapped from Hake so that he could marry her. Ragnhild and Halfdan had a son who was also named Harald.
Halfdan died when he fell through the ice of a lake that had been weakened by cattle dung after a hole was cut in the ice for the cattle to drink. Each of the districts of his kingdom wanted to claim his grave. In the end, it was agreed to divide his body into four pieces so each district could bury a piece of it, resulting in Halfdan's Mounds.