It ain't over till the fat lady sings

The phrase is generally understood to be a reference to opera sopranos, who were typically heavyset.

[2] The imagery of Wagner's opera cycle Der Ring des Nibelungen and its last part, Götterdämmerung, is typically used in depictions accompanying uses of the phrase.

Her farewell scene lasts almost twenty minutes and leads directly to the finale of the whole Ring Cycle.

The first known use in media appeared in the Dallas Morning News on March 10, 1976:[4] Despite his obvious allegiance to the Red Raiders, Texas Tech sports information director Ralph Carpenter was the picture of professional objectivity when the Aggies rallied for a 72–72 tie late in the SWC tournament finals.

He was one of the world’s funniest guys," said Bill, a contender for that title himself.The 1976 use of the phrase was discovered by Fred R. Shapiro, who published it in The Yale Book of Quotations.