Kirszbraun's theorem is one of my favorite theorems in mathematics.
I always wanted to know something about Kirszbraun, or at least to see his picture. Do you have any information about him? (I know only trivial things, like where he was publishing and that he was working in Warsaw.)
Postscript. Thanks to Lukasz Grabowski, I fould the following entry about Kirszbraun in Polish Biographical Dictionary.
Plus, some scanned documents related to Kirszbraun can be requested from USHMM; in particular, there is his picture.