Mayer was born into a Jewish family in a village near Warsaw.
His family was active there in the workers' movement. They
decided to emigrate when Mayer was a child; his father hoped to
find work in Argentina. As a young man, Mayer was arrested for
being a communist. In prison, he organized a hunger strike. The
police released him to keep him from recruiting the other
prisoners to communism. 1933-39: Mayer joined one of the
International Brigades and went to Spain to fight in the civil
war against Franco and fascism in 1936. With Hitler's and
Mussolini's help, the fascists won. Mayer's brigade disbanded,
and he escaped to France, where he continued fighting fascism.
1940-44: Hitler easily defeated France in June 1940. Foreign
Jews, especially communists like Mayer, were now in double
danger. The French suspected foreigners; the Nazis hated Jews.
In 1941, with a number of other Jewish emigres, Mayer joined the
armed French resistance group, Franc-Tireurs et Partisans. For
two years he fought the Nazis but keepi