Upon being informed that the citizens of France had no bread to eat, Marie Antoinette , Queen-consort of Louis XVI of France, exclaimed "let them eat cake", or "Qu'ils mangent de la brioche".
She almost certainly didn't utter the words; critics of the Queen claimed she had in order to make her look insensitive and undermine her position.
The History of the Phrase
There has been some discussion about how "brioche" doesn't translate exactly to cake, but was a different foodstuff (quite what is also disputed), and how Marie has simply been misinterpreted, but the truth is most historians don’t believe Marie uttered the phrase at all.
One reason for this is because variations of the phrase had been in use for decades before she is said to have uttered it, supposed examples of precisely the callousness and detachment of the aristocracy to the needs of the peasants that people claimed Marie had shown by supposedly uttering it. Jean-Jacques Rousseau mentions a variation in his autobiographical 'Confessions', where he relates the story of how he, on trying to find food, remembered the words of a great princess who, upon hearing that the country peasants had no bread, coldly said "let them eat cake/pastry". He was writing in 1766-7, before Marie came to France. Furthermore, in a 1791 memoir Louis XVIII claims that Marie-Thérèse of Austria, wife of Louis XIV, used a variation of the phrase ("let them eat pastry") a hundred years before.
While historians are also unsure if Marie- Thérèse really did say it – Antonio Fraser, a biographer of Marie Antoinette, believes she did - both examples illustrate how the phrase was in use around the time and could have been easily attributed to Marie Antoinette. There was certainly a huge industry devoted to attacking and slandering the Queen, making all sorts of even pornographic attacks on her to sully her reputation. The 'cake' claim was simply one assault among many, albeit the one which has survived most clearly throughout history. The true origin of the phrase is unknown.