Fritz Haber was a German chemist with a Jewish ethnic background. Born in 1868, he was an active scientist between the years of 1891 and his death in 1934, contributing to many important areas of chemistry, for which he won the Nobel Prize in Chemistry in 1918. He was rich and famous throughout his life for his early successes, but had a troubled life which included the suicide of his wife and his expulsion from Germany due to the rise of the Nazi regime. Despite being a Jew hated by Hitler's regime, Haber was among the most patriotic and scientifically productive Germans of the early 20th century.
Along with Carl Bosch, he developed a technique to synthesize ammonia, used for fertilizer, from its elements, and was key to synthesizing poison gases used for warfare in WWI and concentration camps in WWII. Haber is alternately responsible for the lives of millions or even billions which would not have been born if it weren't for the artificial production of fertilizer and its associated agricultural plenty, and the death of millions in the Holocaust.
Haber personally oversaw the release of poison gas on enemy troops during WWI. The horrors of chemical warfare during that era led to treaties to ban the use of biological and chemical weapons, which persist to this very day. Regarding the ethics of chemical war, he said that death was death, and the method of dying did not especially matter. We can see he was wrong by the extended suffering experienced by the targets of poison gas during WWI who did not die.
After WWI, Haber attempted to hatch a scheme to make Germany rich and pay off its war debts by efficiently extracting gold from sea water. His reputation as a scientist allowed him to collect significant funding with which to attempt this, but of course he ultimately failed.
In 1915, in the thick of WWI, his wife, who disapproved of his work creating poison gas, committed suicide in their garden with his military service weapon. He departed the next morning to oversee the release of poison gas. Later, before WWII, Haber was expelled from Germany for his Jewish background, leaving him dejected. He bounced from place to place, spending some time in Oxford, UK, and also the area that today is known as Israel. Shortly after his expulsion, he died sick and unhappy.
Members of his extended family were killed in concentration camps by the poison gas, Zyklon B, which he helped develop. Later, in 1945, at the end of the war, his son Hermann Haber, committed suicide in the United States, possibly due to shame at the evil that his father helped unleash.