SS-Hauptsturmführer (Captain) Karl Fritzsch (10 July 1903 - went missing 2 May 1945), was a German concentration camp officer and deputy, who first suggested and experimented with using Zyklon B gas for the purpose of mass murder.

Karl Fritzsch was born the son of a stove builder in Bohemia, and since the family had to move very often in search of work, he never received a normal school education. For some years Fritzsch worked on ships plying the Danube. His marriage in 1928 to Franzishe Stich produced three children, but ended in divorce in 1942.

In 1930 he joined the Nazi Party and the SS {NSDAP # 261135 SS # 7287} He wanted to make a career in the SS and served at the Dachau concentration camp in 1934.

In May 1940 he became the first Schutzhaftlagerführer (Deputy Commander) to Rudolf Höss at Auschwitz. Here, he very quickly obtained a reputation as the camp horror. Together with Höss, he was responsible for the selection of prisoners to die of hunger as a punishment for the escape of a fellow prisoner. The condemned prisoners were locked in a cell in the basement of the Bunker (the camp prison in Block 11 or 13) until they died of starvation.