The brash, hard-nosed and corrupt leader of the Teamsters union spent four years in prison for charges that included jury-tampering, mail fraud and bribery, before being pardoned by President Richard Nixon in 1971 [source: Time]. Four years later, on July 30, 1975, Hoffa disappeared outside a Detroit-area restaurant where he had gone for a meeting. He was attempting to regain power in the Teamsters, and the most popular theory is that he was killed by mobsters who coveted the union's flush pension fund. Two weeks before his disappearance, federal investigators found out that millions had been stolen from the pension fund [source: Candiotti].
Despite decades of FBI probing, Hoffa's remains have never turned up. Some rumors say that he was buried under the old Giants Stadium in New Jersey, while other stories have his body being fed to alligators in the Everglades or else shipped to Japan inside a compacted junked car. In 2013, FBI agents — following a tip from the alleged former underboss of a Detroit crime family — spent several days excavating a suburban Detroit field, but turned up nothing [source: Tur and Connor].