James Gandolfini, who shot to fame as a mob boss in The Sopranos, died on Wednesday [19] while on holiday in Rome. He was 51.

HBO spokeswoman Mara Mikialian told Reuters on Wednesday evening that a sudden heart attack was the possible cause.

Gandolfini starred in The Sopranos throughout its six-season run and it became a critical and commercial hit, earning the actor three Emmys and a Golden Globe. It also helped to establish the pay-cable network as an original content powerhouse.

The New Jersey native, who began his acting career on the stage in New York, also earned a number of significant film credits. Most recently he appeared in Kathryn Bigelow’s Zero Dark Thirty and was also known for roles in True Romance, Killing Them Softly, Violet & Daisy and UK satire In The Loop.

Gandolfini had been working on a forthcoming HBO show, Criminal Justice.

“We’re all in shock and feeling immeasurable sadness at the loss of a beloved member of our family,” HBO said in a statement.

“He was a special man, a great talent, but more importantly, a gentle and loving person who treated everyone, no matter their title or position, with equal respect.”

Gandolfini is survived by his son Michael from his ex-wife Marcy Wudarski and a daughter Liliana born in 2012 to his second wife Deborah Lin.