Later in life and after his death, Hoover became a controversial figure as evidence of his secretive abuses of power began to surface. He was found to have exceeded the jurisdiction of the FBI‏¹ and to have used the FBI to harass political dissenters and activists, to amass secret files on political leaders,‏² and to collect evidence using illegal methods.‏³ Hoover consequently amassed a great deal of power and was in a position to intimidate and threaten sitting presidents.‏⁴ According to biographer Kenneth Ackerman, the notion that Hoover's secret files kept presidents from firing him is a myth.‏⁵ However, Richard Nixon was recorded as stating in 1971 that one of the reasons he did not fire Hoover was that he was afraid of reprisals against him from Hoover.‏⁶
According to President Harry S. Truman, Hoover transformed the FBI into his private secret police force. Truman stated: "we want no Gestapo or secret police. The FBI is tending in that direction. They are dabbling in sex-life scandals and plain blackmail. J. Edgar Hoover would give his right eye to take over, and all congressmen and senators are afraid of him."‏⁷