How did this expression come to existance (or make sense at all)

Question

How did the expression: "It's not over till the fat lady sings" ever come into existance? Is there any sort of history behind it?

Answer 1

The expression was invented by sportscaster Dan Cook.  His original line was "The opera ain't over till the fat lady sings." This occurred in April, 1978, when he coined the phrase after the first basketball game between the San Antonio Spurs and the Washington Bullets (now the Washington Wizards) during the 1977-78 National Basketball Association playoffs, to illustrate that while the Spurs had won once, the series was not over yet.

Answer 2

Opera.

Answer 3

This phrase in turn refers to the impression by many that at the end of every opera, an aria is sung by a heavy-set woman dressed like a valkyrie. A famous example of this is Wagner's Der Ring des Nibelungen (aka the Ring cycle). This is a set of four separate operas (lasting about 15 hours), in which the final scene includes Brünnhilde (a very large Valkyrie) singing, and then riding onto Siegfried's funeral pyre. The set collapses and the entire cycle ends up in the Rhine river, where it started. The "fat lady" is often illustrated with a horned helmet, a spear, possibly a shield, and possibly blond braids (to suggest Scandinavian ancestry).

from wikipedia