Stefan Hertz was born István Hercz on 21 January 1925 in Oradea (Nagyvárad in Hungarian, Grosswardein in German) in present-day Romania. He was the eldest of three sons of liberal Jewish parents. After attending the Jewish Lyceum, he trained as a toolmaker – a trade that would later save his life.
In the spring of 1944, after Germany occupied Hungary, he was deported with his entire family to Auschwitz. Once there, he was separated from his parents, who did not survive. Stefan Hertz was forced by employees of the Volkswagen plant to work as a fitter in the assembly of V1 flying bombs, first in Fallersleben, then in a satellite camp in Lothringen, and finally, from September 1944, in the Mittelbau-Dora concentration camp in the Harz Mountains. The V1 flying bombs assembled there were primarily fired at London. When the Mittelbau-Dora camp was dissolved, the SS sent Hertz on an evacuation transport in early April 1945 to Bergen-Belsen. After his liberation on 15 April 1945, Stefan Hertz worked for several weeks in the DP camp as a translator for the British liberators. Today he lives in Hungary.