DDT had been discovered in 1874 by a German chemist named Zeidler, but did not have any use for it. In 1939, following on the interest in chemicals due to WWI, Paul MTller discovered that DDT was a very effective insecticide. No effect was apparent on humans. It quickly became the most widely-used pesticide in the world. It was used extensively during World War II by soldiers as well as certain civilian populations to control insect typhus and malaria.