Gad grew up in Berlin. His father was a Jewish immigrant from Austria. Gad's mother had converted to Judaism. The Becks lived in a poor section of Berlin, populated predominantly by Jewish immigrants from eastern Europe. When Gad and his twin sister, Miriam, were 5, the Becks moved to the Weissensee district of Berlin, where Gad entered primary school.

1933-39: I was just 10 when the Nazis came to power. As one of a small number of Jewish pupils in my school, I quickly became the target of antisemitic comments: "Can I sit somewhere else, not next to Gad? He has such stinking Jewish feet." In 1934 my parents enrolled me in a Jewish school, but I had to quit school when I was 12 as they could no longer afford the tuition. I found work as a shop assistant.