Hálfdanar saga Brönufóstra c. 1300 is a legendary saga on Halfdan the son of the legendary king Hringr of Denmark.
In the saga, Halfdan flees his father's kingdom after an attack by the Viking berserker Soti, and goes to live in exile in Bjarmaland. During a sea-voyage he is dragged off course by the witchcraft of a troll named Jarnnef (Iron-Nose) and shipwrecked on the shore of Helluland. Here he rescues the three children of a Scottish earl from the troll and his wife. Halfdan encounters a troll-woman named Brana who is really the daughter of the king of Valland, who was abducted by the troll Jarnhauss (Iron-Skull) and transformed into her current shape. She asks Halfdan and his friends to avenge her by killing Jarnhauss and his fellow trolls. In return, she provides them with shelter, and gives Halfdan a magic ring, a coat that makes him invulnerable to edged weapons, and a dragon-ship. She sends Halfdan to England where he wins the love of Marsibil, daughter of the English king Óláfr, and defeats the schemes of the king's landwarden, Aki, with Brana's magical aid. He marries Marsibil and succeeds Óláfr when he dies. He returns to his father's kingdom and defeats and kills Soti and his Vikings.
It has a sequel in Sörla saga sterka, where it becomes clear that Halfdan is the father of Hogni of the Hjaðningavíg.