TITLE: Who is Kirszbraun?
QUESTION [17 upvotes]: 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.)
P.S. Thanks to Lukasz Grabowski, I fould the following entry about Kirszbraun in Polish Biographical Dictionary.

REPLY [7 votes]: It is very, VERY likely that Kirszbraun published only one paper. Namely, if you read carefully that short entry in Polish (written by E.Marczewski = Szpilrajn), you'll notice that in the penultimate sentence it says that upon completing his studies he got a job as an actuary ("aktuariusz", the person who calculates insurance costs) in an insurance company named "Przyszlosc"; therefore, it is quite reasonable to assume that he didn't continue any form of a(n academic) career as a research mathematician. On the other hand, a footnote an the title page of its Fundamenta paper clearly indicates that the paper is an abridged and improved version of his "Magister" (= Master) thesis, defended back in 1930 and prepared in the preceding 4-year period. So, it is rather safe to jump to the conclusion that Über die zusammenziehenden und Lipschitzschen Transformationen is his only publication, and that he didn't pursued any further mathematical research.