Oppenheimer security clearance hearing
Over four weeks in 1954, the United States Atomic Energy Commission (AEC) explored the background, actions, and associations of J. Robert Oppenheimer, the American scientist who directed the Los Alamos Laboratory during World War II as part of the Manhattan Project to develop the atomic bomb. The hearing resulted in Oppenheimer's Q clearance being revoked.
Source: Wikipedia — Oppenheimer security clearance hearing (CC BY-SA 4.0)