Louis Pasteur is widely recognized for the development of the first vaccine. In the late 19th century, he created the rabies vaccine, building on his earlier work with the anthrax vaccine. Pasteur's pioneering research laid the groundwork for the field of immunology, demonstrating that weakened forms of pathogens could stimulate an immune response in the body. His work not only contributed to public health but also established principles that guided future vaccine development, ultimately saving millions of lives by combating infectious diseases.