Robert von Moschzisker was born on March 6, 1870, in Philadelphia. His father, Franz Adolph von Moschzisker, came of a family of high standing in what was then the Austrian sector of Poland.
An officer in the Austrian army, he joined the forces of Kossuth in the uprising of 1848, was captured as a prisoner of war, escaped to England, taught German literature in King's College, London, studied medicine, and emigrated to the United States to practice his profession. Here he married Clara Harrison, of English descent, by whom he had five children, Robert being the fourth and the youngest of three sons.
Both parents died before the boy was thirteen years old, and he was raised by his father's sister Bertha.