Paul Erdős [also Erdős Pál, Pál Erdős, Erdos or Erdös] (26 March 1913 – 20 September 1996) was an immensely prolific and famously eccentric mathematician who, with hundreds of collaborators, worked on problems in combinatorics, graph theory, number theory, classical analysis, approximation theory, set theory and probability theory.

A standard greeting he would make when he was not contemplating some mathematical problem, as quoted in My Brain Is Open : The Mathematical Journeys of Paul Erdos (1998) by Bruce Schechter, p. 10

Paul Erdős — Response to a question by an agent of the US Immigration and Naturalization Service in 1954 as to what he thought of Karl Marx, often cited as an indication of his detachment from political sensibilities and the situations of the McCarthy era. He was afterwards denied a return visa for re-entering the US until 1959, after attending the International Congress of Mathematicians in Amsterdam; as quoted in The Man Who Loved Only Numbers : The Story of Paul Erd?s and the Search for Mathematical Truth (1998) by Paul Hoffman, p. 128

Paul Erdős — His motto, as he roamed about the world, as the guest of other mathematicians, as quoted in A Tribute to Paul Erd?s (1990) edited by Alan Baker, Béla Bollobás, A. Hajnal, Preface, p. ix

Paul Erdős — SF was an abbreviation for "Supreme Fascist" — the term Erd?s often used to refer to God, as quoted in The Man Who Loved Only Numbers : The Story of Paul Erd?s and the Search for Mathematical Truth (1998) by Paul Hoffman, p. 4

Paul Erdős — Referring to a famous statement by the French anarchist Pierre-Joseph Proudhon that "Property is theft!", as quoted in The Man Who Loved Only Numbers (1998) by Paul Hoffman, p. 7

Paul Erdős — Finally I am becoming stupider no more. — A suggestion for his own epitaph, as quoted in Variety in Religion and Science: Daily Reflections (2005) by Varadaraja Raman, p. 256

Paul Erdős — Common remark when breaking off work for the night, as quoted in "The Magician of Budapest" in The Edge of the Universe : Celebrating Ten Years of Math Horizons (2007) by Deanna Haunsperger and Stephen Kennedy, p. 111

Paul Erdős — Said in regard to any particularly beautiful or elegant proof, referring to a mythical "book" in which God wrote the proofs for all theorems, as quoted in Philosophy of Mathematics (2008) by John Francis, p. 51