The correct answer is option 4, Edward Jenner. Edward Jenner was a British physician who is credited with developing the first successful vaccine for smallpox. Smallpox was a highly contagious and deadly disease that caused significant suffering and death throughout history. Jenner observed that milkmaids who had contracted the less severe disease called cowpox seemed to be protected from smallpox. Based on this observation, Jenner conducted an experiment where he inoculated a young boy with material from a cowpox sore and then exposed him to smallpox. The boy did not contract the disease, thus proving the effectiveness of the cowpox material as a vaccine. This breakthrough in immunization laid the foundation for the eradication of smallpox and revolutionized the field of medicine.