Hi there brudenell!
There was no fat lady, unfortunately. But it seems fairly sure where
the phrase originated...
The chap in question is Dan Cook, a sports commentator. In 1976, in
the San Antonio "News-Express", he wrote in his column that "the opera
ain't over until the fat lady sings" (He now says that he cannot
remember the exact date, or what the column was really about). He then
repeated the line in a 1978 broadcast. The Washington Bullets coach
Dick Motta heard the broadcast, and used the term publicly to
encourage the team's supporters - after which it became the rallying
cry for the rest of the championship. This seems to have been enough
to propel it into the public mind, and get everyone using it.
It's actually rather hard to find this information on the net through
normal searches, so my first tip off was remembering that Cecil Adams
dealt with the question in his excellent "Return of the Straight Dope"
(ISBN 0-345-38111-4). Once I had the name Dan Cook, I used the
"dan cook" fat lady sings
"dan cook" fat lady origin
A few webpages comment that the phrase may have another origin:
"Church ain't over till the fat lady sings". This theory doesn't have
very much backing, however, so I'd stick with the Dan Cook
I hope this helps - feel free to request clarification if anything's
unclear, or the links below do not function properly.
All the best,
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