Gandolfini is believed to have died of a possible heart attack.
“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 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 fronted The Sopranos for six seasons for the cable network, as gangster killer, doting father, and husband prone to infidelity. His performances scored him three Emmy Awards as best lead actor in a drama series.
Since The Sopranos ended Gandolfini has appeared in a number of film roles, including Zero Dark Thirty and the comedy The Incredible Burt Wonderstone.
At the time of his death, he had been working on an upcoming HBO series 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.
The drama is an adaptation of Peter Moffat’s 2008 BBC crime entry and had been in development at HBO for more than a year, earning a pilot order in September when Gandolfini agreed to star.
The future of the project, which would have seen Gandolfini star as Jack Stone, a downtrodden jailhouse attorney who frequents police stations for clients, is now in limbo.
Gandolfini had also signed on in early June to executive produce an adaptation of Canadian comedyTaxi-22 at CBS. He was also developing drama Big Dead Place, based on Nicholas Johnson’s memoir about his work in the U.S. Antarctic Program.