"It ain't over till the fat lady sings." Often quoted as "The opera ain't over till the fat lady sings", and sometimes confused with Yogi Berra's, "It ain't over till its over."
This universal image calls to mind an overweight soprano brandishing a spear and wearing a Viking helmet. It is clearly rooted in Wagnerian opera, specifically "The Ring of the Nibelungen". The "fat lady" is probably best associated with character Brunhilda in "The Valkure", "Siegfreid", or "Twilight of the Gods". At the endings of these operas, Brunhilda is asleep, singing, and dead (respectively); leaving the opera, "Siegfried" as the most logical choice.