Louis Pasteur is known for developing the first vaccine, specifically the rabies vaccine in the late 19th century. His groundbreaking work in microbiology led to the understanding that diseases could be caused by microorganisms. Pasteur’s techniques for cultivating pathogens paved the way for the development of vaccines against various infectious diseases. His rabies vaccine, tested successfully in 1885 on a boy bitten by a rabid dog, marked a significant milestone in medical history and laid the foundation for immunology. Pasteur's contributions continue to impact contemporary vaccine development and public health strategies.