Gunther (Gundahar, Gundahari, Latin Gundaharius or Gundicharius, Old English Gúðere, Old Norse Gunnarr, anglicised as Gunnar) is the German name of a semi-legendary king of Burgundy of the early 5th century. Legendary tales about him appear in Latin, medieval Middle High German, Old Norse, and Old English texts, especially concerning his relations with Siegfried (Sigurd in Old Norse) and his death by treachery in the hall of Attila the Hun.
Despite their new status as foederati, Burgundian raids into Roman upper Gallia Belgica became intolerable and were ruthlessly brought to an end in 436, when the Roman general Aëtius called in Hun mercenaries who overwhelmed the Rhineland kingdom (with its capital at the old Celtic Roman settlement of Borbetomagus, now called Worms) in 437. Gundahar was killed in the fighting, reportedly along with the majority of the Burgundian tribe. (Prosper; Chronica Gallica 452; Hydatius; and Sidonius Apollinaris)
In the Waltharius, Gibicho and his son Guntharius are kings of the Franks, whereas the king of the Burgundians is named Heriricus who is father to Hiltgunt, the heroine of the story. Hagen appears here as a kinsman of Gibicho and Guntharius, but the relationship is not made explicit. In their combats with Waltharius, Guntharius loses a leg, Hagen loses half his face and one eye, and Waltharius loses a hand. But there is no hint in later tales that Gunther is in any way maimed. Another version of the story of Waltharius and Hiltgunt appears in the Norse Thidreks saga, but in this account Gunther plays no part at all.
Gunther otherwise only appears in tales relating to Siegfried and the fall of the Niflungs. In most texts, such as the Nibelungenlied, Gunther/Gunnar seeks to make Brünhild his wife, but can win her and master her only because the hero Siegfried/Sigurd aids him and takes his place. Siegfried marries Gunther's sister Kriemhild/Gudrun. An impassioned debate between Brünhild and Kriemhild about their respective status leads to the secret that Siegfried had taken Gunther's place being revealed. Gunther then agrees to assist in Siegfried's murder. After Siegfried is murdered, Gunther and his brothers, despite deep suspicions of treachery, accept an invitation from Etzel, or Atli in Old Norse (i.e. Attila the Hun), to visit his court. There Gunther and his brothers were betrayed. In some versions of the story, they were thrown in a snake pit to die, while in others they were killed fighting the Huns and their allies.
According to the Atlamol Gunnar remarried after Brynhild's death to a woman named Glaumvor.