Robert Koch was a pioneering German physician who made groundbreaking discoveries in the field of microbiology in the late 19th century. Some of his key accomplishments included: 1) Establishing the germ theory of disease and demonstrating that specific diseases are caused by specific microorganisms like anthrax, tuberculosis, and cholera. 2) Developing techniques to isolate and grow bacteria in pure culture, allowing him to prove their role in causing illness. 3) Formulating Koch's postulates, a set of criteria for establishing causation between a microbe and a disease.