Charles “Chuckie” O’Brien, a longtime associate of Teamsters boss Jimmy Hoffa died Thursday, Feb. 13, in Boca Raton, Florida, the Associated Press reports.

O’Brien became a leading suspect in the labor leader's disappearance and later was portrayed in the Martin Scorsese film “The Irishman.”

O'Brien's stepson said he died from what appeared to be a heart attack. He was 86.

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

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

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

In an interview with The Associated Press in 2006, O’Brien denied having anything to do with Hoffa’s disappearance and said he didn’t think the mystery of his death would ever be solved.