J. Edgar Hoover

John Edgar Hoover (1 January 1895 - 2 may 1972) was the first Director of the Federal Bureau of Investigation (FBI) of the United States. Appointed director of the Bureau of Investigation—predecessor to the FBI—in 1924, he was instrumental in founding the FBI in 1935, where he remained director until his death in 1972 at age 77. Hoover is credited with building the FBI into a larger crime-fighting agency, and with instituting a number of modernizations to police technology, such as a centralized fingerprint file and forensic laboratories.

Villainy
However Hoover had a darker side, during his time in his position, on multiple occasions he abused his power. There are reports of him blackmailing politicians, unfairly (and sometimes illegally) persecuting political dissidents (most famously Martin Luther King Jr). Other cases include falsely framing Ma Barker as a crime boss, to cover up her being killed in a crossfire, with a shootout with the Barker Gang. He also ruined the careers and reputations of several other agents, such as Melvin Purvis so he could claim the credit for the there work himself. There were also other rumors of he himself being blackmailed by the mob.

Some conspiracy theorists speculated that he was involved in the Assassination of John F. Kennedy or helped cover up the trail of the real killers and have Lee Harvey Oswald framed for the assassination. However, there is little, if any, hard evidence to back up these theories.

Links
J. Edgar Hoover on Real Life Heroes wiki