John Edgar Hoover (1895-1972)

Head of the FBI during 48 years, he was a controversial figure for his authoritatrian style and his use of rather shady methods, whether against criminals or his own employees. Despite his apparently restless war against crime gangs in the 30’s, which allowed him to expand his agency’s powers considerably, he will later be suspected of protecting organized crime by systematically minimizing the importance of their activities and influence. Some will go as far as pretending that the Mafia blackmailed Hoover, threatening to reveal his alleged homosexuality, a method Hoover himself favoured to maintain his power. Many U.S. Presidents — he lived through 8 different White House administrations — pondered getting rid of him as head of the FBI but gave up on the idea. On two occasions, Richard Nixon had summoned him to the Oval Office with this goal in mind, but twice Hoover came out of the President’s office still in post. Hoover personally led the Bureau’s investigation on Kennedy’s death, but the report of the House Select Committee on Assassinations will conclude that the FBI had willfully neglected to investigate on the possibility of a conspiracy in the matter, and also that the agency had failed in communicating crucial informations to other agencies and departments.

Source:
http://en.wikipedia.org/wiki/Edgar_Hoover