The German mythological figure Brünnhilde is a Valkyrie, an athletic equestrian and favorite daughter of Wotan, chief of the gods. Kiefer's work "Brünnhilde Schläft" (Brünnhilde Sleeps) alludes to an episode recounted in the second opera of Richard Wagner's "Ring" cycle. After Brünnhilde betrays Wotan, he sadly puts her to sleep and surrounds her with a ring of fire, declaring that only a man who does not fear his spear may walk through it to rescue her.