G.C. Rota, on being assigned to help check the problems of <i>Linear Operators</i> for Dunford and Schwartz as a graduate student at Yale (while it was still a manuscript), but finding himself unable to solve one of the problems:<p><i>After a few hours, feeling somewhat downcast, we all got up and left. The next morning I met Jack, who patted me on the back and told me, "Don't worry, I could not do it either." I did not hear about Problem Twenty of Section Nine for another three years. A first-year graduate student had taken Dunford's course in linear operators. Dunford had assigned him the problem, the student had solved it, and developed an elegant theory around it. His name is Robert Langlands.</i><p>(From <i>Indiscrete Thoughts</i>, p. 37.)
He deserves it! A great thinker! Here's a series of lectures he gave outlining some great fundamentals of his view on mathematics ( with very little prerequsites ). - <a href="https://video.ias.edu/The-Practice-of-Mathematics" rel="nofollow">https://video.ias.edu/The-Practice-of-Mathematics</a>
And here's his original letter to Weil.<p><a href="https://publications.ias.edu/rpl/paper/43" rel="nofollow">https://publications.ias.edu/rpl/paper/43</a>