Felix Hausdorff managed to withstand World War I in Greifswald, but WWII took its toll on him. During Nazi rule he was forced to retire in 1935, then failed to emigrate to the USA, and finally in 1942 suicided together with his wife after receiving notice of their upcoming internment in Endenich.

He was still actively working in those years, despite having to live in harsh conditions under the dictatorship and not being allowed to publish in Germany. Besides papers in Fundamenta Mathematicae (e.g. this), his Nachlass shows that he kept working in topology and set theory almost until the very end. See also this question.