Leo Szilard, a Jewish physicist and inventor born in Budapest to religious Jews, had a hand in some of the 20th century’s most crucial—and deadly—inventions.
After a childhood in Hungary, Szilard moved to Berlin in 1919 where, under the tutelage of Albert Einstein (who sang Szilard’s praises for his work on thermodynamics), he conceived the electron microscope—and helped Einstein invent a refrigerator with no moving parts.
Szilard left for England after Hitler’s rise to chancellor, urging family and friends to do the same. After this, Szilard produced his most notable work: the conception of a nuclear chain reaction which, according to historian Richard Rhodes, “saw a way to the future, death into the world and all our woes—the shape of things to come.”
On that note, Szilard co-authored with Einstein a letter to FDR in 1939 warning that Germany might develop A-bombs so the U.S. should do the same. Thus began the Manhattan Project.
Like Oppenheimer, Szilard later expressed regret at his involvement in nuclear armament, publishing a collection of short fiction that explored his own role in nukes, curiously titled The Voice of the Dolphins. You’ll have to read it to see why.