Born in New York City on 2 December 1923, the child of Greek parents, Maria Anna Sophie Cecilia Kalogeropoulos had, by the mid-1950s, transformed herself from a fat, frumpy Wagnerian Valkyrie into a slim, svelte bel canto soprano the two syllables of whose (newly shortened) name will forever spell out the words "dramatic truth".
The voice itself was remarkable - at once raw and rich; utterly unmistakable, often unpalatable; always recognisable and yet infinitely adaptable in its chameleon-like ability to change colour and character from role to role. Once heard, never forgotten. No wonder the Italians called her La Divina.
But then there was the temperament - the fiery Greek fury that got her dubbed "The Tigress" (we owe that tag to a backstage paparazzo shot), drove rifts between her and her management and, long after she had retired from the stage, typecast her on screen as Pier Paolo Pasolini's vengeful Medea.
For 10 brief years she impassioned the operatic stage, striking terror into the eardrums of mere "canary-fanciers", instilling theatre into the mere black-and-white of the score, and then she was gone, lured by Onassis into a life of sybaritic abandon, thrown over when Jackie Kennedy hove into view, ending her days a recluse in a Paris apartment.
So it was that Diana and La Divina have been linked together in death. But who can say if their names will still be linked another 20 years from now? For, even as cynical record executives concede that the People's Princess may well have faded from the collective memory before Christmas comes - and that Elton John's "Candle in the Wind (1997)" will almost certainly be knocked from its No 1 slot as soon as the next Spice Girls song appears - for countless thousands of opera fans across the world, history is still divided not into BC and AD, but BC and AC - Before and After Callas. And EMI is this week re-issuing another nine complete opera sets and 13 recital discs to remind a new generation of opera-lovers why Maria is always with us.