The most poisonous and lethal chemical on earth is Botulinum toxin.
Just 1 nanogram per kilogram can kill a healthy human. It first it was discovered as cause of food poisoning in the late 18s due to incorrectly prepared sausage in Germany.
But later Professor Emile Van Ermengem first isolated the bacterium Clostridium botulinum.
Despite how dangerous and lethal this chemical is today it is used by many people who want to “freeze” their faces from getting old by injecting very small doses of it.
The modern medicine calls it Botox.