Heinrich Zangger, professor at the University of Zurich and one of the leading Swiss forensic medical specialists, comes into contact with Einstein because of their common interest in Brownian motion. They become close friends, who also remain in constant communication on scientific, political, academic, and personal topics during Einstein’s time in Berlin.

Zangger not only advises Einstein on issues of academic appointments but on personal matters, too. In particular he acts as a mediator after Einstein’s separation from his wife Mileva, and sometimes takes care of Einstein’s sons.