Fritz Haber is the inventor of synthetic ammonia. This breakthrough meant that food yields were no longer limited by the amount of natural nitrogen deposits. Our modern food production system, and all of its incredibly high yields, are due to this invention. Without the ability to synthesize our fertilizer, literally billions of people would not be alive today.
He is also the founder of modern chemical warfare. He lead German teams in WWI in the development of chlorine gas and, to make it worse, he actually would show up in the battlefield to supervise its use. His chemical work also eventually led to developing the chemicals used in the Nazi gas chambers.
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