Ernst Sejersted Selmer (11 February 1920 – 8 November 2006) was a Norwegian mathematician, who worked in number theory, as well as a cryptologist. The Selmer group of an Abelian variety is named after him. His primary contributions to mathematics reside within the field of diophantine equations. He started working as a cryptologist during the Second World War; due to his work, Norway became a NATO superpower in the field of encryption. Biography Early life Ernest S. Selmer was born in Oslo in the family of Professor Ernst W. Selmer and Ella Selmer (born Sejersted). He was the brother of Knut S. Selmer who married with Elisabeth Schweigaard, as well as first cousin of Francis Sejersted. Already early in school, Selmer demonstrated mathematical talent. When attending Stabekk high school he was an editor of the school's magazine Tall og tanker (numbers and thoughts). In 1938, he won Crown Prince Olav's Mathematics Prize for high school graduates. From 1942–1943, he studied at the University of Oslo. As a student at the university during World War II, Selmer was involved in encrypting secret messages for the Norwegian resistance movement. During the autumn of 1943 when the Germans forced the University to close he escaped to Sweden, just in time before the Nazi Germany secret police Gestapo closed the university and arrested the male students. In 1944 Selmer was sent to London, where he took technical responsibility for all Norwegian military and civilian cipher machines. The communication was mainly carried out using the Hagelin cipher machine. When the war ended, Selmer returned to Norway, and in 1946, was hired as a lecturer in the University of Oslo. In the same year, he started working for the Cipher Department of the Armed Forces Security Service as a consultant. With colleagues, he built a communication system for Norway's equivalent of the MI5, which was used from 1949 till 1960. Selmer spent the spring of 1949 at the Cambridge University working with the famous mathematician JWS Cassels. As a result of their collaboration, a group related to an Abelian variety—namely, the Selmer group—was discovered and named after Selmer. In 1993, Andrew Wiles used Selmer's group in his proof of the Fermat's last theorem. Middle years Selmer received his dr.philos in 1952 from the University of Oslo and was at the same time hired as a lecturer for the university. Among Selmer's lectures, his lectures on data