Hoss was assigned in 1940 to become the first commandant of the newly established Auschwitz concentration camp. Once installed in his new post, where he would serve for three and a half years, Hoss proceeded to develop Auschwitz from an old army barracks into a sprawling death camp.
Hoss is also credited with perfecting the process of mass extermination. It was through his influence that the Nazis moved from primitive forms of gassing to the use of Zyklon B, a crystalized form of prussic acid that proved to be much more efficient.
On April 2, 1947, Hoss was convicted at Nuremberg of war crimes and crimes against humanity, for which he was sentenced to death. His execution was carried out on April 16, 1947, when he was brought to Auschwitz and hanged on the site of his crimes.