Arne Beurling
Arne Carl-August Beurling (February 3, 1905 – November 20, 1986) was a mathematician and professor of mathematics at Uppsala University (1937-1954) and later at the Institute for Advanced Study at Princeton, USA.
Arne Beurling worked extensively in harmonic analysis, complex analysis and potential theory.
In 1940 he single-handedly decyphered and reverse-engineered an early version of the Geheimfernschreiber (one of the "Fish cyphers") used by Nazi Germany, and created a device that enabled Sweden to decypher German teleprinter traffic passing through Sweden from Norway on a cable. In this way, Swedish authorities knew about Operation Barbarossa before it occurred. This became the foundation for the Swedish Swedish National Defence Radio Establishment (FRA).
Arne Beurling's great-grandfather was Per Henric Beurling (1758 (or 1763) – 1806), who founded a high quality clock factory in Stockholm in 1783.