Karl Ludwig Föppl (27 February 1887 in Leipzig – 13 May 1976 in Munich) was a German mechanical engineer who succeeded his father, August Föppl as Professor of Technical Mechanics at the Technical University of Munich.
During World War I, Föppl worked as a cryptanalyst.
During World War II he worked as a mathematician and cryptographer, initially in Inspectorate 7/VI, and later in the war within General der Nachrichtenaufklärung.Since 1940, he has been a full member of the Bavarian Academy of Sciences.
Föppl was one of the earliest cryptoanalysts in the Germany Army, working at this profession during both the first and second world wars, eventually becoming Chief of Sixth Army’s Evaluation Office.
His work was kept secret from both his family and his colleagues, even his assistant Friedrich L.
Bauer, who would also become a well known cryptologist, never knew.
The work of Hilmar-Detlef Brückner of the Bavarian State Archive (German: Bayerisches Hauptstaatsarchiv) brought Föppl to prominence.
After he died, more of his papers were eventually brought to the light by his daughter Liselotte; they were called Lebenserinnerungen: Ludwig Föppl and fleshed out the work of Brückner by providing details of Föppl's work during World War I.