Joan Ruth Bader was born on March 15, 1933, in the New York City borough of Brooklyn, the second daughter of Celia (née Amster) and Nathan Bader, who lived in the Flatbush neighborhood. Her father was a Jewish emigrant from Odessa, Ukraine, then in the Russian Empire, and her mother was born in New York to Austrian Jewish parents. The Baders' older daughter Marylin died of meningitis at age six, when Ruth was 14 months old. :3 The family called Joan Ruth "Kiki,” a nickname Marylin had given her for being "a kicky baby. ” :3 When "Kiki" started school, Celia discovered that her daughter's class had several other girls named Joan, so Celia suggested that the teacher call her daughter "Ruth" to avoid confusion. :3 Although not devout, the Bader family belonged to East Midwood Jewish Center, a Conservative synagogue, where Ruth learned tenets of the Jewish faith and gained familiarity with the Hebrew language. :14–15 At age 13, Ruth acted as the "camp rabbi" at a Jewish summer program at Camp Che-Na-Wah in Minerva, New York.