John Edgar Hoover (January 1, 1895 - May 2, 1972), known popularly as J. Edgar Hoover, was the Director of the Federal Bureau of Investigation (FBI) of the United States. He founded the present form of the agency, and remained director for 48 years until his death. During his life, Hoover was highly regarded by much of the U.S. public. Since his death, various allegations have tarnished this image.

Hoover's leadership spanned eight presidential administrations, encompassed Prohibition, the Great Depression, World War II, the Korean War, the Cold War, and the Vietnam War. During this time, the United States moved from being a rural nation with strong isolationist tendencies to an urbanized superpower.

From nearly the beginning of his career with the FBI, Hoover was accused of exceeding and abusing his authority, criticism that grew especially strong in the 1960s. He is known to have investigated individuals and groups because of their political beliefs rather than their suspected criminal activity, as well as using the FBI for other illegal activities, such as burglaries and illegal wiretaps. Hoover frequently fired FBI agents by singling out those who he thought "looked stupid like truck drivers" or he considered to be "pinheads." He also relocated agents who had displeased him to career-ending assignments and locations. Melvin Purvis was a prime example; he was one of the more effective agents in capturing and breaking up 1930s gangs and received substantial public recognition, but a jealous Hoover maneuvered him out of the FBI. It is because of Hoover's long and controversial reign that FBI directors are now limited to 10-year terms.