Steg was born on 27 January 1925 in
Czechoslovakia into a family of Orthodox Jews. His father, Mordechai Steg, born on 19 April 1895 in
Bistra,
Austria-Hungary, took his family to
Paris in 1928. Mordechai had three children with his wife, Feige: Adolphe, Bitia, and Rachel. Steg's father, Mordechai, who had gone by the name of Martin to avoid identification as a Jew, was interned at the
Beaune-la-Rolande internment camp. He was then subsequently deported to
Auschwitz as part of Convoy No. 5 on 28 June 1942. Martin survived deportation and later returned to Paris. Adolphe, a student at the Lycée Voltaire, bore a
yellow badge as required for Jews living in German-occupied territory. However, his teacher, Mr. Binon, had his class read
De la tolérance by
Montesquieu. He escaped the
Vel' d'Hiv Roundup on 16 July 1942 with false papers, and, thanks to a smuggler, was able to cross the
demarcation line into the
Zone libre. He was saved by and his brother , who housed Jewish people fleeing from the Nazis in
Cazaubon. He was then sent to
Sarlat to continue his education, where he joined the 3rd Battalion of Armagnac of the
French Forces of the Interior. ==Medical career and leadership in the Jewish community==