John Snow was a British physician and a pioneer in the field of epidemiology. He is best known for his work during the Cholera outbreak in London in 1854, where he mapped the cases of the disease and identified a contaminated water pump on Broad Street as the source of the outbreak. His efforts helped to improve public health and sanitation practices. Snow's innovative approach to disease tracking laid the groundwork for modern public health measures. He is often referred to as the "father of modern epidemiology" for his contributions to understanding how diseases spread and for advocating for the importance of clean water.