A few days ago I took the plunge and finally saw "The Imitation Game", a Hollywood movie that is supposed to be about the mathematicians who broke The Enigma, or the German encryption machine during WWII, which the German military used to communicate with evil axis troops.
The movie was loosely based on a biographical novel called The Enigma about one of these Mathematicians: an Englishman named Alan Turing, who is also known as the father of artificial intelligence, and the father of computing in general.
In a true Hollywood manner, the movie gave all credits for the breaking of the Enigma to the English Mathematicians without mentioning the enormous accomplishment of the Polish Mathematician Marian Rejewski.
Marian Rejewski was the first person to apply Pure Mathematics to cryptanalysis. In that sense Marian Rejewski is the father of mathematical cryptanalysis.
For centuries before Marian Rejewski, the most reliable way of breaking an encrypted text was by analyzing the frequency of the occurrence of certain letters in the encrypted texts and comparing these to the most frequently occurring letters in plain texts, which was a purely linguistic approach.
The purely linguistic approach did not work when it was applied to messages encrypted with the Enigma, and this gave the Germans a head start in the war. The Enigma was deemed unbreakable.
Marian Rejewski applied a fairly new-ish branch of Mathematics to decipher messages composed through the Enigma. This branch of Mathematics, namely Group Theory, is still used today in cryptography and cryptanalysis, and in particular, Group Theory is at the heart of the RSA problem.
The main goal of Group Theory, as I was once told by a prominent researcher, is to classify the various different types of mathematical structures called groups, and the field itself is highly abstract so applying results from it to real life problems back then was rather revolutionary.
In other words, Marian Rejewski was a creative genius who risked his own life to save the lives of others. When Germany took over Poland he went to France and brought his work with him, and when Germany took over France, he fled to Britain and gave his work to the British Intelligence, who passed it on to The Bletchley Park and Alan Turing and his team.
After the war Rejewski returned to the family that he left in order to save the families of others and became an accountant.
Even I only heard of Rejewski a few years ago when an Australian friend of mine with Polish background posted about Rejewski on his Facebook timeline. Then I took a course called Codebreakers & Codemakers: An Introduction to Cryptography, and I learned more about this remarkable man who appears to be forgotten by the masses he saved.