It ain't over till the fat lady sings
Nothing is irreversible until the final act is played out.
Just to get this out of the way before we start: is it 'til, till or until? You can find all of these in print:
It ain't over 'til the fat lady sings
It ain't over till the fat lady sings
It ain't over until the fat lady sings
You might even find versions with isn't instead of ain't. Grammarians argue about 'til and till; I'm opting here for till.
Okay; so who was the fat lady? If we knew that, the origin of this phrase would be easy to determine. Unfortunately, we don't, so a little more effort is going to be required. The two areas of endeavour that this expression is most often associated with are the unusual bedfellows, German opera and American sport.
The musical connection is with the familiar operatic role of Brunnhilde in Richard Wagner's Götterdämmerung, the last of the immensely long, four-opera Ring Cycle. Brunnhilde is usually depicted as a well-upholstered lady who appears for a ten minute solo to conclude proceedings. 'When the fat lady sings' is a reasonable answer to the question 'when will it be over?', which must have been asked many times during Ring Cycle performances, lasting as they do upwards of 14 hours. Apart from the apparent suitability of Brunnhilde as the original 'fat lady', there's nothing to associate this 20th century phrase with Wagner's opera.
All the early printed references to the phrase come from US sports. Some pundits have suggested that the phrase was coined by the celebrated baseball player and manager, Yogi Berra, while others favour the US sports commentator, Dan Cook. Berra's fracturing of the English language was on a par with that of the film producer Sam Goldwyn but, like those of Goldwyn, many of the phrases said to have been coined by him probably weren't. Along with "It's déjà vu all over again" and "The future isn't what it used to be", Berra is said to have originated "The game isn't over till it's over". All of these are what serious quotations dictionaries politely describe as 'attributed to' Berra, although he certainly did say "You can observe a lot by watching", at a press conference in 1963. In any case, "the game isn't over till it's over" isn't quite what we are looking for, missing as it is the obligatory fat lady.
Dan Cook made a closer stab with "the opera ain't over till the fat lady sings", in a televised basketball commentary in 1978. Cook was preceded however by US sports presenter Ralph Carpenter, in a broadcast, reported in The Dallas Morning News, March 1976:
Bill Morgan (Southwest Conference Information Director): "Hey, Ralph, this... is going to be a tight one after all."
Ralph Carpenter (Texas Tech Sports Information Director): Right. The opera ain’t over until the fat lady sings."
Another US sporting theory is that the fat lady was the singer Kate Smith, who was best known for her renditions of "God Bless America". The Philadelphia Flyers hockey team played her recording of the song before a game in December 1969. The team won and they began playing it frequently as a good luck token. Smith later sang live at Flyer's games and they had a long run of good results in games where the song was used. Sadly, Ms. Smith sang before games, not at the end. If the phrase were "It ain't started until the fat lady sings", her claim would have some validity.
Whilst printed examples of the expression haven't been found that date from before 1976, there are numerous residents of the southern states of the USA who claim to have known the phrase throughout their lives, as far back as the early 20th century. "It ain’t over till the fat lady sings the blues" and "Church ain’t out till the fat lady sings" are colloquial versions that have been reported; the second example was listed in Southern Words and Sayings, by Fabia Rue and Charles Rayford Smith in 1976.
Carpenter's and Cook's broadcasts did popularise the expression, which became commonplace in the late 1970s, but it appears that we are more likely to have found the first of the mysterious fat ladies in a church in the Deep South than on the opera stage or in a sports stadium.
See also: the List of Proverbs.