Fritz Haber and the twentieth century

"A German Jewish scientist, his invention with his brother-in-law Carl Bosch of the Haber-Bosch process, to make ammonia fertiliser, enriched the whole world. Estimates of the number of people who are alive today on account of his invention are in the hundreds of millions, and even in the billions. What a great benevolence to mankind, you might say, what a saviour of lives! But the same man was also responsible for the invention of chemical warfare. He not only invented chlorine gas but personally supervised its use against English and French troops at Ypres in 1915. His creation of nitric acid for explosives and his ammonia fertilisers were said by Max Planck to have prolonged the First World War by a full year. His life story is thus one of the most conflicted you could ever possibly come across. He hoped by his contributions to the war effort to prove himself a German patriot despite being a Jew; but his wife, who was also a scientist, was so distressed by his work on chemical warfare (not to mention his disregard of her career) that she shot herself on the day he was promoted to the rank of captain. Worse was to follow. After the First World War, Haber led the team that invented the cyanide-based insecticide Zyklon B. It was this chemical that was used to murder vast numbers of Jews in the Nazi death camps during the Second World War. It seems fitting that as we draw to the end of this chapter, we face a final war-related irony: that the man who saved more lives than anyone else was also responsible for millions of deaths."

Ian Mortimer in Centuries of Change:
Which Century Saw the Most Change and Why it Matters to Us (2014)
[review here]