Hiltgunt Margret Zassenhaus (10 July 1916 – 20 November 2004) was a German philologist who worked as an interpreter in Hamburg, Germany during World War II, and later as a physician in the United States.

[2][3] Her brothers were the mathematician Hans (known for the butterfly lemma and the Zassenhaus group), and physicians Günther and Willfried.

[4] Instead of censoring the mail, she added messages urging the recipients to send food or warm clothing.

[4][9] Zassenhaus maintained her own records in order to keep track of where the prisoners were being held; these files became important for the later evacuation by the White Buses in 1945.

[2][3][10] With the war in Europe nearing its end, Zassenhaus learned of "Day X", when all political prisoners were to be killed.

After the war, Zassenhaus was unable to complete her studies at the University of Hamburg due to the damage inflicted on the city.

[14] Zassenhaus is the only person from Germany decorated with the Royal Norwegian Order of St. Olav for her activities during World War II.