Paul Hermann Müller was a Swiss chemist, awarded the Nobel Prize in Physiology or Medicine in 1948 for his discovery of the insecticidal properties of dichlorodiphenyltrichloroethane (DDT). After graduating in chemistry from the University of Basel, he joined the company J.R. Geigy AG, where his task was to develop new synthetic pesticides. In 1939, after testing hundreds of substances, he discovered that DDT, a compound first synthesized in 1874 but whose biological properties had never been studied, was a highly potent contact poison against a wide variety of arthropods, including mosquitoes, flies, and lice. His discovery had a revolutionary impact on public health and was widely used to combat insect-borne diseases such as malaria and typhus, especially during and after the Second World War. The Nobel Committee recognized his work as fundamental to protecting human health and increasing agricultural production, awarding him the prestigious recognition.