MONTREAL -- Most people know Joseph Pistone by the name of his alter-ego, "Donnie Brasco." And many of those who do, want to kill him.

A self-described "street guy" who became famous when he struck at the heart of New York's notorious organized crime families, the former FBI undercover agent's story enthralled moviegoers when it was chronicled in the 1997 movie "Donnie Brasco," starring Johnny Depp.

His knowledge of organized crime brought him to Quebec's inquiry into construction-industry corruption as an expert witness Monday. He was testifying from behind a TV screen and there was a media publication ban on details of his appearance.

Usually, Pistone shuns the limelight -- and for good reason.

The Mob put a $500,000 bounty on his head after he skilfully infiltrated their ranks, posing as a bar-hopping jewel thief between 1976 and 1981.

Even the FBI, where he's a legend, only has an old, blurry surveillance photo of him on its website where it describes his pioneering undercover work.

Pistone, whose insinuation into the Bonanno and Colombo crime families led to 200 indictments and more than 100 convictions, rarely sticks his head up. When he does, it's with his appearance altered and under tight security.

He lives under an assumed name in an undisclosed location and has a licence to pack a gun.

A consultant to the justice system, he has written several books, both fiction and non-fiction, including a novel with the son of Mob kingpin Joe Bonanno.

Pistone was such a good undercover agent that surveillance teams from the FBI and New York City police, who weren't in the loop, had Brasco listed as an associate of the Bonannos.

The Bonanno family has been linked to Montreal's Rizzutos -- and it's unclear whether Pistone's testimony will delve into those ties. Quebec's Charbonneau inquiry is examining corruption in the construction industry and its connection to politics and organized crime. Pistone began with a detailed description of how he infiltrated the Mafia and faced potential threats to his life, from the get-go.

"What I have to do is give you the mindset of gangsters," he testified, "and how they operate."

After they were arrested, Mob kingpins were stunned when FBI agents told them whom they had befriended. The man who had brought Pistone into the Mob was later found murdered.

The FBI has warned Mob chieftains that anyone who harms Pistone will face the bureau's wrath.

"It's not the wiseguys I'm most worried about," Pistone told National Geographic News in 2005.

"They respect me. They know I just did my job. I never entrapped anyone, never got them to do something they wouldn't have done anyway.

"But there's always the chance of running into someone who thinks he's a cowboy, you know, someone who doesn't like what you did."

Pistone, who quit the FBI in 1986, summed up the Mob philosophy in an interview with He described how one of his criminal associates replied when asked why he would want to be "a wiseguy."

"He says, 'Donnie, you can lie, you can steal, you can cheat, you can kill -- and it's all legitimate,"' Pistone quoted the man saying. "In their world, it's all legitimate. That's how they think."

Born in Erie, Pa., Pistone grew up in a tough, working-class Italian neighbourhood in Paterson, N.J. His dad owned a bar and he has described his mom as a religious woman.

He graduated from college with an education degree in 1965 and was a teacher for a year before joining the Office of Naval Intelligence.

The father of three children says he always wanted to be a cop.

He joined the FBI in 1969, working in a variety of jobs before being transferred to New York in 1974 to combat truck hijackers. That led to his first undercover operation.

Pistone, who could drive 18-wheel trucks and bulldozers, worked his way inside a large and lucrative gang that stole heavy vehicles and equipment.

When police moved in on the gang in February 1976, Pistone's work led to 30 arrests.

He thought his next job would be targeting crooks who sold items from hijacked trucks -- and he expected the assignment to last about six months.

It wound up lasting six years and it sent shockwaves through the Mafia.

Pistone's Sicilian heritage, fluency in Italian and acquaintance with gangsters and their codes of conduct from his old neighbourhood made him a natural choice for the case.

It didn't hurt that he said he never sweated under pressure.

Pistone underwent extensive preparation, including FBI gemology classes so he could pass as "Donnie the Jeweller."

All traces of his old life were wiped out when he went undercover. Not even close friends and colleagues knew where he'd gone.

At the end of the operation, he got a $500 bonus.

"As an undercover agent, you don't expect anything," he told National Geographic News. "You just do your job."