Johannes Anton Marquart or possibly Marquardt (born 27 September 1909 in Erolzheim in Germany) was a German actuarial and insurance mathematician.
During World War II, Marquart was employed into the Germany Army Inspectorate 7/VI, in 1940, which would later become the General der Nachrichtenaufklärung.
He would eventually become head of Referat Ia of Group IV of the organization in November 1944 engaged in research into German Army hand cryptographic systems.
Prior to that period Marquart had been chief cryptanalysis in KONA 5.