Shiro Ishii 石井 四郎 (25 June 1892 – 9 October 1959) was a medical officer for the JapaneseKwantung Army during the Second Sino-Japanese War who became interested in germ warfare. He established Unit 731 in 1936 to conduct secret investigations into biological warfare. Unit 731 operated a massive complex in rural Manchukuo where Ishii supervised brutal unethical experiments on live human test subjects, mostly prisoners of war.
After Japan's defeat at World War II, ample evidence existed to try Ishii for war crimes, but the United States government granted him legal immunity for his atrocities in exchange for access to the findings of his research. Accounts of Ishii's postwar career are contradictory, but agree that he died of throat cancer in 1959 at the age of 67.
Shiro Ishii was the commandant of the Unit 731 facility at Pingfan, Manchukuo. Sergeant Hideki Fujita, who was stationed at Pingfan without knowing its purpose, found Ishii an impressively vigorous administrator and an intimidating figure, much more so than he would have expected from a physician. He knew only that Ishii was engaged in some sort of scientific research that far exceeded his own very limited knowledge of that subject.