Without the innovations of one Nobel Prize-winning scientist, about half of the world's population would not be alive. So why aren't we celebrating Fritz Haber day every year? Well, to put it bluntly, it's because he was also something of a terrible human being.

The good

Fritz Haber, born in Germany in 1868, grew up in a world where food production still heavily relied on turnips, ground-up skeletons, poop, pee, and turnips that had been turned into poop by way of the digestive system. 

A good supply of nitrogen in the soil is essential for plant growth. As farmers and scientists realized this over the centuries, different regions developed different systems for getting this vital nutrient back into the depleted soil following several harvests.

 In 17th century England, there was the incredibly sexy Norfolk four field crop rotation, which reintroduced nitrogen into the soil by planting turnips on years where they would previously have had to leave the field fallow (a fancy farmer word for "empty") to recover. In America, bison bones were used as fertilizer, before they were hunted nearly to extinction in the 19th century. Then, of course, there was the old-fashioned method of just cramming a field full of as much poop and pee as you can manage (or, of course, harvest guano).

As the population exploded during industrialization, it became clear there was going to be a problem. People feared that the food supply would not continue to keep up with demand, in part due to the limited supply of nitrogen. 

Some, like Thomas Malthus, believed that the problem would sort of "solve" itself. Though he realized that technological advances would increase production, he believed this would lead to population growth, bringing standards of living back to roughly to the "everyone is starving" levels they were at pre-increase.

"Famine seems to be the last, the most dreadful resource of nature. The power of population is so superior to the power of the earth to produce subsistence for man, that premature death must in some shape or other visit the human race," Malthus wrote in an essay that frankly could be a speech delivered straight to the camera by Thanos. 

"The vices of mankind are active and able ministers of depopulation. They are the precursors in the great army of destruction; and often finish the dreadful work themselves. But should they fail in this war of extermination, sickly seasons, epidemics, pestilence, and plague advance in terrific array, and sweep off their thousands and tens of thousands. Should success be still incomplete, gigantic inevitable famine stalks in the rear, and with one mighty blow levels the population with the food of the world."

While many were happy with merely letting populations sort themselves out through famine, disease and death, along came several scientists who helped remove the production part of the production and distribution problem. Attempts were made by others, but the most successful process for creating an artificial fertilizer came from Fritz Haber. 

In 1909, he created the Haber Process (later known as the Haber-Bosch process) for making ammonia – a key ingredient in fertilizer and a compound of nitrogen and hydrogen – in industrial quantities. Nitrogen, though it makes up around 78 percent of the atmosphere, is a very stable element and not prone to reacting with other elements, so this was no small feat. 

Carl Bosch (yes, of the company Bosch) acquired the method from Haber, and refined it, replacing Haber's original expensive and rare catalysts with methods that were much cheaper and abundant. He and his team carried on refining the process, until it could produce enough ammonia to be used the world over as a fertilizer, feeding half the world.

The bad

Look, it gives us no pleasure to point to the guy who allowed us to feed half the planet and say "this is a terrible human being" but he basically was. Haber, known for his work feeding the world, is also known as the father of chemical warfare.

During World War I, he set his mind and lab to weaponizing chlorine gas, with one test causing "the deaths of several German troops". When he was satisfied that the gas was usable as a weapon, he found that generals and officers – people whose day-to-day job was to kill people – were reluctant to use it.

"[General] Falkenhayn revealed to us that a new weapon, poison gas, was to be used and that my corps area had been selected for the first attempt," Infantry General Berthold von Deimling wrote of the plan to test Haber's new product.

"The poison gas would be delivered in steel cylinders, which would be built into the trenches and opened when the winds were favorable. I must confess that the commission for poisoning the enemy, just as one poisons rats, struck me as it must any straightforward soldier: it was repulsive to me. If, however, the poison gas were to result in the fall of Ypres, we would win a victory that might decide the entire campaign. In view of this worthy goal, all personal reservations had to be silent. So onward, do what must be done! War is necessity and knows no exception."

Haber even went to the front line in Ypres and smoked cigars while he awaited the first of many chlorine gas attacks on Allied troops. When the wind was right to take the gas towards the enemy, they released it. Within minutes, about 10,000 soldiers were asphyxiating horribly, and a few minutes later they were dead.

A Canadian soldier who was there that day described the effects of the gas as “an equivalent death to drowning only on dry land."

"The effects are there—a splitting headache and terrific thirst (to drink water is instant death), a knife edge of pain in the lungs and the coughing up of a greenish froth off the stomach and the lungs, ending finally in insensibility and death. It is a fiendish death to die."

Another witness – a British soldier far enough away to survive the attack – described the chaos that followed.

"[I watched] figures running wildly in confusion over the fields. Greenish-gray clouds swept down upon them, turning yellow as they traveled over the country blasting everything they touched and shriveling up the vegetation," he wrote. "Then there staggered into our midst French soldiers, blinded, coughing, chests heaving, faces an ugly purple color, lips speechless with agony, and behind them in the gas soaked trenches, we learned that they had left hundreds of dead and dying comrades"

Following the success of the attack – if it can be called that – Germany ramped up the use of the gas. By the time the war was over, around 1.3 million casualties had been caused by chemical weapons, and around 90,000 excruciating deaths.