Marcus Klingberg, Polish-Israeli physician and biologist (born 1918)

Avraham Marek Klingberg, known as Marcus Klingberg, was a Polish-born Israeli epidemiologist and the highest ranking Soviet spy ever uncovered in Israel. Klingberg made major contributions in the fields of infectious and noninfectious disease epidemiology and military medicine, while simultaneously passing intelligence to the Soviet Union regarding Israel's biological and chemical warfare capacities. Declared the "most important Soviet spy in Israel" by the Jerusalem Post, Klingberg is regarded as causing the greatest damage ever to the country's national security interests.