He first developed the technique of vaccination.

Explanation

Edward Jenner is considered the pioneer of the vaccination technique. In 1796, he demonstrated that exposure to cowpox could provide immunity to smallpox, laying the foundation for modern immunology. The other options, while significant figures in biology, are not linked to the original development of vaccination. Louis Pasteur later expanded upon Jenner's work, Gregor Mendel is known for genetics, and Beadle & Tatum are known for their genetic research.