Correct Answer:

Landsteiner

Solution : The correct option is Landsteiner.

Karl Landsteiner, an Austrian immunologist and pathologist, discovered blood groups in the early twentieth century. In 1901, he discovered the ABO blood type system, which lay the groundwork for modern understanding of blood compatibility and transfusion. Landsteiner's finding was a tremendous step forward in medicine, with far-reaching ramifications for blood transfusions, organ transplants, and genetics.