Hoover emphasized modern technological investigative techniques, improved training, and obtained increased funding from Congress. During the 1930s, FBI exploits against notorious gangsters made him a national hero. In the 1940s and 1950s he became well known for his anti-Communist and anti-subversive views and activities. At the same time, he consciously failed to restrict Mafia activity, which was conducted with minimal interference from the FBI.

For decades Hoover denied the existence of the Mafia, permitting it to flourish until the 1970's. This would be bad enough, but it's not his worst legacy. That would be permitting the use of law enforcement as an instrument of revenge and politics, a behavior which reached its apex in the Nixon administration. In the 1960s Hoover became a problematic political figure due to his lack of sympathy for the civil rights movement and the Kennedy administration. His reputation declined in later years following revelations concerning his vendettas against liberal activists and widespread illegal FBI activities.

Behind the scenes he had a habit of crossdressing, as he was spotted more than once wearing an ill-fitting cocktail dress, lisping and prancing around at private parties with boyfriend Clyde Tolson, hosted by the Mob. Hoover published a number of books detailing his work with the FBI. His writings include “Persons in Hiding” (1938), “Masters of Deceit” (1958), “A Study of Communism” (1962) and “Crime in the United States” (1965). Hoover died on May 2, 1972.