Frithiof is the main character of a legendary saga from Iceland that dates to c.1300. Frithiof “the bold” was the son of King Thorstein and the bravest among men. He had been raised together with a girl name Ingeborg by their foster-father Hilding. Both Frithiof’s and Ingeborg’s paternal fathers die in war, and Ingeborg’s two brothers (now kings) become jealous with Frithiof's excellent qualities. They deny him Ingeborg's hand and take her to another kingdom. Still, Frithiof visits Ingeborg and they continue to love each other.
The two evil brothers then send Frithiof away to another kingdom to take tribute. While he is away, they burn down his homestead and marry Ingeborg to an older king named Ring. When Frithiof returns with the tribute and learns about what has transpired, he leaves the country and becomes a Viking. After three years he returns, and spends a winter with the dying king Ring. Ring appoints Frithiof earl and makes him the care-taker of his child with Ingeborg. After Ring dies, Frithiof and Ingeborg marry and he becomes the king of Ringerike. He then declares war on Ingeborg's brothers, killing one of them with his sword, Angervadil, and making the second one his vassal.