Updated

The FBI has spent this week digging up a field in suburban Detroit for the remains of former Teamsters union leader Jimmy Hoffa, who disappeared 38 years ago. He was last seen outside a restaurant about 20 miles from the digging site where he was to meet with a New Jersey Teamsters boss and a Detroit Mafia captain.

Here's a look at Hoffa, his legacy and the enduring mystery of his disappearance.

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Q: Who was Jimmy Hoffa, and why was he such a big deal in labor?

A: Though a grade-school dropper, James Riddle Hoffa was a tough negotiator who formed his own union and merged it with the Teamsters when he was 19. In 1957, at age 44, Hoffa was elected the Teamsters president, a union he built to become the nation's largest in the country by 1968 with 2 million members, according to the Teamsters website. He continued as Teamsters president even in prison, until he officially resigned in 1971 when his jury tampering sentence was commuted by President Richard Nixon.

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Q: Did he become a household name after he was reported missing, or was he widely known before that?

A: As Teamsters president, Hoffa was the face of the union. He earned the loyalty of his members with contracts that improved their standard of living dramatically. It was under Hoffa that the Teamsters won their first national trucking contract. He was an acquaintance of mobsters and was last seen July 30, 1975, outside the Machus Red Fox restaurant in Oakland County, north of Detroit. Hoffa was supposed to meet that day with Anthony "Tony Jack" Giacalone, a figure in the Detroit mob. Anthony "Tony Pro" Provenzano, a New Jersey Teamsters leader, also was believed to be in on the meeting.

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Q: What was Hoffa's most famous or infamous accomplishment before 1975 when he was reported missing?

A: Hoffa found an enemy in Robert F. Kennedy, who had been counsel to a congressional committee investigating the unions and later became U.S. attorney general. Kennedy had accused Hoffa of corruption and connections to the mob. Hoffa was put on trial in 1962, accused by Kennedy of taking payoffs from trucking companies. That ended in a hung jury, but two years later in Nashville Hoffa was convicted of jury tampering. In 1967, Hoffa went to jail, sentenced to 13 years for jury tampering and fraud. He refused to give up the Teamsters presidency. He quit the position in 1971, and President Richard Nixon pardoned him.

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Q: What does the FBI think happened to him?

A: The FBI believes Hoffa was killed. He was declared legally dead in 1982. Donald "Tony The Greek" Frankos told Playboy magazine in 1989 that mob leaders tried to dissuade Hoffa from retaking control of the Teamsters after his release from prison. But Hoffa refused and allegedly threatened to tell authorities about mob infiltration of the unions. Frankos claimed Hoffa was killed by members of the Westies, a New York Irish gang, on the orders of Genovese crime family boss Anthony "Fat Tony" Salerno. His body was cut up in Michigan, then driven to New Jersey several months later and buried in the concrete foundation of the sprouting Giants Stadium, Frankos said. He even claimed to know what area of the stadium: a section near the corner of the west end zone. Retired FBI agent Jim Kossler has said Frankos was not reliable.

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Q: It seems like the FBI conducts a search for his body every year. How much taxpayer money is spent on the effort?

A: To give you an idea of how much has been spent trying to solve the mystery, from the time of Hoffa's disappearance in 1975 through 1985, more than 200 FBI agents were assigned to the case in New Jersey, Detroit and at least four other cities. During the period, more than 70 volumes of files were compiled, containing more than 16,000 pages. A failed two-week search for Hoffa's body in 2006 on a Michigan horse farm alone cost about $250,000.

But Keith Corbett, a former federal prosecutor in Detroit who was active in Mafia prosecutions touching on the Hoffa case, said it was appropriate for the FBI to act on what they deem credible tips despite the dead ends they repeatedly hit.

"Anytime you look for somebody and don't find the body it is embarrassing," Corbett said. "The thing the public isn't aware of, but police know, is there are a lot of dead ends in an investigation."

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Q: What's become of the Teamsters?

A: The union now has about 1.4 million working members and 500,000 retirees in the U.S. and Canada, and is led by Hoffa's son, James P. Hoffa. He had challenged and lost to Ron Carey in 1996 during Carey's re-election run for Teamsters president. Carey was forced from office a year later after his campaigned was charged with illegally using about $885,000 in funds. Hoffa won the seat in 1998.