Step 1: Concept
Louis Pasteur was a French biologist who pioneered the principles of vaccination and pasteurization.
Step 2: Analysis
Smallpox was famously addressed by Edward Jenner. Pasteur worked on several vaccines, including those for chicken cholera and anthrax.
Step 3: Reasoning
His most significant contribution to human medicine was the development of the rabies vaccine in 1885.
Step 4: Conclusion
Louis Pasteur developed the Rabies vaccine.
Final Answer: (D)