James Gandolfini, the burly actor best known for his Emmy-winning portrayal of a conflicted New Jersey mob boss in the acclaimed HBO cable television series "The Sopranos," died on Wednesday (June 19) while vacationing in Rome, the network said.

Gandolfini, 51, who began his career in theatre in New York, making his Broadway debut in a 1992 revival of "A Streetcar Named Desire," died of a possible heart attack, HBO spokeswoman Mara Mikialian said.

Since "The Sopranos" ended its six-season run in June 2007, Gandolfini has appeared in a number of big-screen roles, including the espionage thriller "Zero Dark Thirty" and the comedy "The Incredible Burt Wonderstone."

At the time of his death, Gandolfini had been working on an upcoming HBO series titled "Criminal Justice." HBO declined to elaborate on the series other than to say that it was in development and that Gandolfini was a part of it.

Gandolfini broke ground with his signature portrait of Tony Soprano, the head of a fictional New Jersey mob family, in "The Sopranos."

The show, which earned Gandolfini three Emmy Awards as best lead actor in a drama series, was considered by many critics at the time the finest drama to have aired on U.S. television.

Gandolfini's role also paved the way for a parade of popular prime-time shows built around profoundly flawed characters and anti-heroes, from "Dexter" and "Breaking Bad" to "Mad Men" and "Nurse Jackie."

Presented by Adam Justice