He gave lectures on category theory in the forests surrounding Hanoi while the city was being bombed, to protest against the Vietnam War (The Life and Work of Alexander Grothendieck, American Mathematical Monthly, vol. 113, no. 9, footnote 6).
EDIT: That behaviour show what having a conscience means when you take it to the limit, which -to me- is really inspiring...
It is not only that. He left the IHES as a protest because it was partially founded by the NATO.
For non-specialists, the IHES is equivalent in 'scientific value' to any Insitute of your choice: Princeton, the Newton Institute, Max Planck, CERN... whatever. It is one of the few 'best of the best'.
He just left.
He became a recluse long ago, but that does not diminish his scientific merits.
He gave lectures on category theory in the forests surrounding Hanoi while the city was being bombed, to protest against the Vietnam War (The Life and Work of Alexander Grothendieck, American Mathematical Monthly, vol. 113, no. 9, footnote 6).
Wow, just wow...