At the end of WW1, most of warring nations had developed gas warfare techniques and had phosgene, mustard, chlorine and Lewisite gases. Mustard was the easiest to handle and use, but after the war, no further development happened to them. There was little interest because no one in 1919, suspected another world war would be caused by a young ex-corporal named Adolf Hitler by 1939.
By necessity, Germany in the 30's started to look for better insecticides and weed killers to help their own crop production. By 1938, a chemist, Dr. Gerhard Schrader discovered ethyl dimethyl amido phosphor cyanidate. It proved to be an excellent insecticide. As research continued and tests conducted, it was found it might be used as a military weapon. The name given to it was "Tabun" and a special factory was created to make it near Wroclaw, Poland. The new gas was so dangerous that it was not until 1942 before the Germans had created a safe factory to make it on a larger scale. Production began at the rate of 1000 tons a month and by the time the Russians had captured, over 15000 tons of Tabun had been made. The Russians knew nothing about the gas, but dismantled the entire factory and shipped back to Russia and took all of the Tabun without telling the Allies.
But the offspring of the initial newly discovered insecticide also led to isopropyl methyl phosphoro flouridate. This was even more effective as chemical weapon. The research team called it, "Sarin". The Germans drew up plans to produce it but it was a WAY more dangerous gas to handle and produce in large quantities. But, a pilot plant was built in Anorganawerk, and only a small amount was ever produced.
As 1942 turn into 1944, the chemists who had discovered the new chemical weapons by mistake, continued to create chemical cocktails and their final disccovery, pinacolyl phoshoro fluoridate, proved to more deadly and fragile to make. They called it, "Soman". This weapon never got into production.
When the Allies reached various ammo dumps in Germany in 1945, they eventually would stumble onto a million shells and over 100,000 aircraft bombs filled with Tabun around Dyhernfurth. According to those in charge of the ammo dumps, none of them were intended to be used against the enemy but were filled only to put the Tabun into containers to use up production chemical stock. Only a few hundred of shells or bombs discovered contained Sarin and Soman, 30 times more lethal than Tabun. These agents were nerve gases.
Soman and Sarin can kill someone in less than two minutes after exposure. Even some of the compounds used to make the nerve gas can cause the "Gulf War Syndrome" to those exposed to them in insecticides and this did occur to German farmers.
Despite the discovery of new weapons, Hitler was very apprehensive in using them at all. His personal experience in WW1 with gas influenced him, but the Germans had no antidote for any of the new gases. Since not everything was known about them, except how to make them and what they do, one mistake could cause a fiasco with no way to handle it. Another reason was that of retaliation by the Allies using gas also.
The person who discovered them would eventually work for the US Army creating the same gases in the 1950's.