Who was the director of the FBI known for investigating alleged radicals?

J. Edgar Hoover served as the first Director of the FBI from its establishment in 1935 until his death in 1972. He is particularly known for his controversial leadership style and for implementing many modern investigative techniques within the bureau. One of the most significant aspects of his tenure was the focus on investigating alleged radicals, which included surveillance of civil rights leaders, activists, and political dissidents during the Red Scare and the Civil Rights Movement. Hoover's actions during this time have been criticized for infringing on civil liberties and for maintaining extensive files on individuals he deemed subversive or a threat to national security. His legacy continues to influence discussions around the balance between security and civil rights in policing and intelligence operations.