Theiler, TAY lur, Arnold (1867-1936), was a South African veterinary research scientist who carried out pioneer studies of the tsetse fly and how it spread sleeping sickness. He also studied the effects of poisonous plants on animals, animal diseases, and animal diets. In 1908, Theiler established the Onderstepoort Veterinary Institute in Onderstepoort (north of Pretoria), South Africa. This institute has an international reputation for veterinary science.