John was the youngest child of a farming family from East Anglia. His mother took in a wounded Thorfinn in 1008, which proved to be their village's undoing when Askeladd's band subsequently raided the village.
John died of a fever in 1006. Two years later his father was called up to the fyrd and was not at home when Thorfinn, who was scouting the area for Askeladd, was injured while fleeing from soldiers. John's mother and sister took Thorfinn in after discovering him on a riverbank and he was given John's clothes to wear while he was washed. It is implied that Thorfinn strongly resembled John, as the latter's clothes, though a bit large, fit him, and he too had a tendency to scratch at his head when there were fleas on him. It was while John's mother was combing Thorfinn outside that a soldier came by to warn of a Viking spy who had infiltrated the area. She covered for Thorfinn by claiming that he was John.
That night, Thorfinn tried to warn the mother and sister to flee the area before running out and giving the signal to Askeladd's band, who were offshore in their longships. The mother called after him by her son's name before discovering how dangerous he was after seeing that he had killed three soldiers before swiftly dealing with a fourth in front of her. When the Vikings arrived to raid the village, she could only stand rooted in shock. The mother and her daughter's fates are unknown but they are presumed to have been killed in the raid.