Paul Halmos (1916-2006) was an American mathematician born in Hungary. He worked in probability there, statistics, operator theory, ergodic theory, and functional analysis. He received the AMS Steele Prize for exposition. Three of his books include How to Read Mathematics, How to Write Mathematics, and How to Speak Mathematics.
Halmos enjoyed taking photos of mathematicians everywhere he traveled. In 2011, the Archives of American Mathematics digitized some of his collection. More information about this project can be found at http://mathdl.maa.org/mathDL/46/?pa=content&sa=viewDocument&nodeId=3801. You can also view an index of photos at http://mathdl.maa.org/mathDL/46/?pa=content&sa=viewDocument&nodeId=3887.
I am very thankful to this wonderful collection of photos of a multitude of mathematicians. Do you have a favorite photograph from this collection or other collections?