Shiro Ishii 石井 四郎 (25 June 1892 – 9 October 1959) was a medical officer for the Japanese Kwantung 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.