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"Who said I may not agree with what you say but I will defend to the death your right to say it?
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Though these words are regularly attributed to Voltaire, they were first used by Evelyn Beatrice Hall, writing under the pseudonym of Stephen G Tallentyre in "The Friends of Voltaire" (1906), as a summation of Voltaire's beliefs on freedom of thought and expression.

Another possible source for the quote was proposed by Norbert Guterman, editor of "A Book of French Quotations," who noted a letter to M. le Riche (February 6, 1770) in which Voltaire is quoted as saying: "Monsieur l'abbé, I detest what you write, but I would give my life to make it possible for you to continue to write" ("Monsieur l'abbé, je déteste ce que vous écrivez, mais je donnerai ma vie pour que vous puissiez continuer à écrire"). This remark, however, does not appear in the letter.


voltare
Voltaire is most often credited with the saying, but many believe that this is a widespread mistake, and that the quote was originally said by Ewelyn Beatrice Hall. There is no definite answer to this question."

I always thought it was Voltaire.