The discovery of M. leprae by G. H. Armauer Hansen (1841–1912) in 1873 represents a link in a chain of development in international medicine that was influenced by two main concepts, namely, that germs may be causes of disease and that social conditions may be related to disease, either as causes or consequences or both. Hansen's work is also a link in a chain of research on leprosy in Norway. Hansen met with serious challenges in addition to those that were purely scientific. To prove the causative effect of the microorganism according to principles that later came to be known as Koch's postulates, Hansen felt compelled to conduct experiments that were deemed illegal by the authorities. At the same time, he was fighting to establish priority for his discovery. Later, Hansen was honored as the discoverer of the bacillus of leprosy and was privileged to see benefits in the public health as a consequence of the discovery. Hansen's epoch-making achievements may serve as an inspiration to all who aspire to combat disease by seeking answers to questions about causes of disease, modes of prevention, and social consequences of disease.