In Norse mythology, Brynhildr was a shieldmaiden and a valkyrie. She is a main character in the Völsunga saga and some Eddic poems treating the same events. Under the name Brünnhilde she appears in the Nibelungenlied and therefore also in Richard Wagner's opera cycle Der Ring des Nibelungen. Brynhildr is probably inspired by the Visigothic princess Brunhilda of Austrasia, married with the Merovingian king Sigebert I in 567. The history of Brynhildr includes fratricide, a long battle between brothers, and dealings with the Huns.

According to the Völsungasaga, Brynhildr is the daughter of Budli. She was ordered to decide a fight between two kings: Hjalmgunnar and Agnar. The valkyrie knew that Odin himself preferred the older king, Hjalmgunnar, yet Brynhildr decided the battle for Agnar. For this Odin condemned the valkyrie to live the life of a mortal woman, imprisoned her in a remote castle behind a wall of fire on top of mount Hindarfjall in the Alps, and cursed her to sleep until any man would rescue and marry her. The hero Sigurdr Sigmundson (Siegfried in the Nibelungenlied), heir to the clan of Völsung and slayer of the dragon Fafnir, entered that ring and awoke Brynhildr by removing her helmet and cutting off her chainmail armour. He immediateley fell in love with the shieldmaiden and proposed to her with the magic ring Andvarinaut. Promising to return and make Brynhildr his bride, Sigurdr then left her castle and headed for the court of Gjuki, the king of Burgundy.

According to the Völsunga saga, Brynhildr bore Sigurdr a daughter, Aslaug, who later married Ragnar Lodbrok. In the Nibelungenlied, Brünnhilde is instead the queen of Isenland (Iceland).