Ruth Popper, née Kauders was born in Bad Kissingen on September 15, 1920 as the first child of the merchant Josef Kauders and his wife Käthe, née Siedner. The family owned a shop in Ludwigstrasse. Between April 1931 and September 1933, she attended Kissingen Realschule. 

After the Nazis’ seizure of power, the family saw themselves increasingly exposed to the arbitrariness of the Nazi authorities. Ruth’s father Josef Kauders was taken into “Schutzhaft” (protective custody) as early as on March 17, 1933 together with seven other Kissingen Jews. Ruth Popper remembers the arrest of her father: “When I think of it, it is like a nightmare. I was 13 years old and on March 17, a young guy in uniform came into our shop and said to my father: ‘You are arrested, without any reason, simply because you are a Jew!’ I was caught completely by surprise: My father in prison! Many Jewish men had been taken into the bicycle cellar of our school, then into the prison.” (Personal report by Ruth Popper, Geneva, letter to Hans-Jürgen Beck from September 30, 1985). In her later letters, she emphasizes – just like her younger brother Alex – the commitment of the headmaster Dr. Robert Hofmann who had bravely stood up for his imprisoned father: “My father was a diabetic and, risking his own life, Herr Direktor Hofmann made it possible that I could take food to my father. He was the only person who made me trust someone in a world that was breaking down for me!” (Ibid.)

When the situation for Jewish families got more and more dangerous, the Kauders made up their minds to leave Bad Kissingen. As early as in September 1933, their parents unsubscribed Alexander and his sister Ruth from Kissingen Realschule and the family moved to Hamburg, Josef Kauders’ city of birth. But in June 1934 they returned to the spa town once more, before leaving for good. In the middle of the 1930s, they first took their children to Hindenburg in Upper Silesia for some weeks, a city about 150 kilometres south east of Wroclaw (Breslau), where Josef Kauders’ mother owned a grocery shop. From there, the family moved to Hamburg, Josef Kauders’ birthplace and two years later they moved their place of residence to Berlin.Ruth Kauders was able to flee to England. She married the banker and photographer Heinz H. Weissenstein from Holzminden and they had a son Herbert Franklin. Later, Ruth got divorced and married the diamond dealer Leopold Popper (1904-1983) from Vienna. They had five children. In 1998 Ruth Popper visited her birthplace with her son Thomas again and met Kissinger acquaintances. She died in May 2003 in Geneva at the age of 82.