This is a picture of Alexander Grothendieck, taken near the end of his life:
I took this picture of a page in a book that was just lying around in Oberwolfach a couple of weeks ago (I think the book was published by the Fields Institute). Unfortunately, I failed to note down an exact attribution -- if anyone knows the name of this book/the photographer, please let me know.
EDIT: Commenter DH writes that the source of this photo is Masters of Abstraction, by photographer Peter Badge.