(CNN) -- James Gandolfini, best known for his role as an anxiety-ridden mob boss on HBO's "The Sopranos," died in Italy, possibly of a heart attack, an HBO spokeswoman and the actor's managers said Wednesday. He was 51.
Gandolfini was on holiday in Rome, said Mara Mikialian, HBO's vice president for program publicity.
The actor was scheduled to make an appearance at the Taormina Film Fest in Sicily this week, according to the festival.
Gandolfini won three Emmy Awards for his portrayal of Tony Soprano, the angst-ridden mob boss who visited a therapist and took Prozac while knocking off people. "The Sopranos" aired from 1999 to 2007.
"Jimmy was the spiritual core of our Sopranos family, and I am stunned at this devastating loss," said Chris Albrecht, the former president of HBO who gave the green light to "The Sopranos." "He was a great talent, but an even better man. My thoughts are with his family."
Gandolfini was born September 18, 1961, in Westwood, New Jersey, according to Biography.com.
He graduated from Rutgers University and, as the story goes, he worked as a bartender and a bouncer in New York City until he went with a friend to an acting class.
He got his start on Broadway, with a role in the 1992 revival of "A Streetcar Named Desire" with Jessica Lange and Alec Baldwin.
Gandolfini's big screen debut came in the role of a heavy in the bloody "True Romance" in 1993. His breakthrough came on the small screen in 1999 with the role of Tony Soprano.
"He was a genius. Anyone who saw him even in the smallest of his performances knows that," David Chase, who developed "The Sopranos," said in a statement. "...A great deal of that genius resided in those sad eyes."
Gandolfini, who was notoriously press shy, had a reputation in the tabloids for being sometimes difficult.
"He wasn't easy sometimes. But he was my partner, he was my brother in ways I can't explain and never will be able to explain," Chase said.
While Gandolfini was known for sometimes ruthless, often imposing characters, those who worked with him described an actor who put his heart into a role.
"He was just so good at the emotion. A very passionate man and a very, very tender man," Matthew Warchus, who directed Gandolfini in the 2009 Broadway play "God of Carnage," told CNN. "I really loved him and admired him a great deal."
Gandolfini's acting credits included roles in "The Last Castle" with Robert Redford, "The Mexican" with Brad Pitt and Julia Roberts and "Surviving Christmas" with Ben Affleck.
In recent years, he had starred in several movies, including the Oscar-nominated "Zero Dark Thirty," "The Taking of Pelham 1 2 3" and "Killing Them Softly."
News of the actor's death spread quickly, drawing shock and sadness from those who had worked with him.
"James Gandolfini was a kind, funny, wonderful guy. I'm so lucky to have worked with him. Sending love to his family. Such a sad, sad day," Olivia Wilde, who starred with the actor in "The Incredible Burt Wonderstone," said in a post on Twitter.
Actor Steve Carrell, who also appeared in the movie, simply said on Twitter: "James Gandolfini. What a great loss."
Gandolfini is survived by his wife, Deborah, and their 9-month-old daughter, Liliana. He is also survived by a son, Michael, from another marriage.
CNN's KJ Matthews, Douglas Hyde, Elise Miller and Henry Hanks contributed to this report.