International Vegetarian Union (IVU)
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History of Vegetarianism - Europe: The Middle Ages to the 18th Century
Rene Descartes (1596-1650)

From the Souvenir Book of the 1957 IVU Congress in India:

RENE DESCARTES, the French Philosopher, never touched meat.

This seems a little extreme, but the 1911 Encyclopeadia Brittanica stated:

At his first coming to Franeker he arranged to get a cook acquainted with French cookery; but, 2 Ouvres, v. 255. 8 Ib. vi. 199. to prevent misunderstanding, it may be added that his diet was mainly vegetarian, and that he rarely drank wine.