Charles “Chuckie” O’Brien, a long-time associate of Jimmy Hoffa who became a leading suspect in the US union leader’s disappearance and was portrayed in Martin Scorsese film The Irishman, has died at the age of 86.

His stepson, Harvard Law School professor Jack Goldsmith, said in a blog post that Mr O’Brien died in Boca Raton, Florida, from what appeared to be a heart attack.

Mr O’Brien was a constant companion to Mr Hoffa in the decades when the labour leader developed the Teamsters into one of the largest and most powerful unions in the nation from the late 1950s to the early 1970s.

After Mr Hoffa’s still-unsolved disappearance in 1975, Mr O’Brien became a leading suspect when the federal government publicly accused him of picking up Mr Hoffa and driving him to his death.

Prof Goldsmith called the accusation untrue. “But practically everyone believed it,” he added.

Charles O’Brien at the federal court building in Detroit
Charles O’Brien at the federal court building in Detroit (Richard Sheinwald/AP)

FBI agents questioned Mr O’Brien about the death at least a dozen times.

In an interview with the Associated Press in 2006, he denied having anything to do with Mr Hoffa’s disappearance and said he did not think the mystery would ever be solved.

He said he viewed Mr Hoffa as a father figure. He was a child when the union supremo took him in along with his mother.

“It’s very frustrating. I have so much inside, my love for him and his family,” Mr O’Brien said.

Mr Hoffa was Teamsters president from 1957 to 1971. The FBI has said his disappearance was probably connected to his attempts to regain power in the union.

It was known that he intended to give evidence to a special Senate investigative panel, known as the Church Committee, about Mafia involvement in US-backed plots to assassinate Cuban President Fidel Castro, Mr O’Brien told the AP.

He was born in Kansas City, Missouri, in 1933. As a young child, he moved to Detroit with his mother after his father abandoned the family, and his mother became friends with the Hoffa family.

When Mr Hoffa became president of the union, Mr O’Brien became his special assistant at the age of 23, according to Prof Goldsmith.

“They were so close, and Hoffa treated Chuckie with such affection that many people thought Hoffa was his biological father,” he said.

In the 2019 Scorsese film, Mr O’Brien was portrayed by actor Jesse Plemons.

Mr O’Brien is survived by his wife Brenda, a daughter and four sons and stepsons.