into the family of Shmuel Dantzig (?-1940) and Guta Dimant (1863-1917), he grew up in Lódz and studied mathematics with Henri Poincaré in Paris. His brother Jacob (1891-1942) was murdered by the Nazis during the Holocaust; he also had a brother Naftali (who lived in Moscow) and sister Emma.

Tobias married a fellow Sorbonne University student, Anja