Ofterdingen and Kropotkin

Nicolas Bourbaki, one of the great mathematicians of the twentieth century, did not exist. He was the collective name of a small group of boisterous French who determined in the 1930s to rewrite the moribund university syllabus, starting from the barest principles and definitions and working upwards: "Euclid for the next 2000 years." [...]

When an article by the non-Bourbakian Ralp Boas appeared in the Encyclopaedia Britannica explaining that the man was in fact a collective pseudonym, Boas received a letter from Bourbaki, from his "ashram in the Himalayas". "You miserable worm", it began, "how dare you say that I do not exist". "Here", observed Boas, "Bourbaki was displaying less than his usual precision of language, since I had not asserted his non-existence, only his non-individuality". Bourbaki then started a rumour that Boas did not exist.

Alexander Masters, "The many in the one", TLS April 18 2008, p.29