Johann Heinrich Füssli in the context of "The Nightmare"

In poetry and literature, a shade (translating Greek σκιά, Latin umbra) is the spirit or ghost of a dead person, residing in the underworld.

An underworld where the dead live in shadow was common to beliefs in the ancient Near East. In Biblical Hebrew, it was called tsalmaveth (צַלמָוֶת: lit. "death-shadow", "shadow of death") as an alternate term for Sheol. The Witch of Endor in the First Book of Samuel notably conjures the ghost (owb) of Samuel.

In ancient Greek cult practice and literature, a nekyia or nekya (Ancient Greek: νέκυια, νεκυία; νεκύα) is a "rite by which ghosts were called up and questioned about the future," i.e., necromancy. A nekyia is not necessarily the same thing as a katabasis. While they both afford the opportunity to converse with the dead, only a katabasis is the actual, physical journey to the underworld undertaken by several heroes in Greek and Roman myth.

In common parlance, however, the term "nekyia" is often used to subsume both types of event, so that by Late Antiquity for example "Olympiodorus ... claimed that three [Platonic] myths were classified as nekyia (an underworld story, as in Homer's Odyssey book 11)".

Gudrun (/ˈɡʊdruːn/ GUUD-roon; Old Norse: Guðrún) or Kriemhild (/ˈkriːmhɪlt/ KREEM-hilt; Middle High German: Kriemhilt) is the wife of Sigurd/Siegfried and a major figure in Germanic heroic legend and literature. She is believed to have her origins in Ildico, last wife of Attila the Hun, and two queens of the Merovingian dynasty, Brunhilda of Austrasia and Fredegund.

In both the Continental (German) and Scandinavian traditions, Gudrun/Kriemhild is the sister of the Burgundian king Gunther/Gunnar and marries the hero Siegfried/Sigurd. Both traditions also feature a major rivalry between Gudrun and Brunhild, Gunther's wife, over their respective ranks. In both traditions, once Sigurd has been murdered, Gudrun is married to Etzel/Atli, the legendary analogue of Attila the Hun. In the Norse tradition, Atli desires the hoard of the Nibelungen, which the Burgundians had taken after murdering Sigurd, and invites them to his court; intending to kill them. Gudrun then avenges her brothers by killing Atli and burning down his hall. The Norse tradition then tells of her further life as mother of Svanhild and enemy of Jormunrekr. In the continental tradition, Kriemhild instead desires revenge for her brothers' murder of Siegfried, and invites them to visit Etzel's court intending to kill them. Her revenge destroys both the Huns and the Burgundians, and in the end she herself is killed.