I appeal to the philosophers of all countries to unite and never again mention Heidegger or talk to another philosopher who defends Heidegger. This man was a devil. I mean, he behaved like a devil to his beloved teacher, and he has a devilish influence on Germany. … One has to read Heidegger in the original to see what a swindler he was.
As quoted in "At 90, and Still Dynamic : Revisiting Sir Karl Popper and Attending His Birthday Party" by Eugene Yue-Ching Ho, in Intellectus 23 (Jul-Sep 1992)