Tributes poured in on social media, describing Gandolfini as jovial and likable.
Actor Mark Ruffalo shared his grief on Twitter: "Oh Jimmy. It's a crying shame. You stormed in and out. Your voice like velvet granite. From a whisper to a shout. A comet of a man."
'He lit up the room with a big smile'
Even after his "Sopranos" fame, he was very down to earth, said iReporter Pat Tantalo, who worked on the set of a 2006 movie Gandolfini starred in.
He lit up the room with a big smile the first time he walked into the production office, Tantalo recalled.
"We instantly connected. He planted his huge mitts on my shoulders and called me a little bull."
Tantalo posted a goodbye tribute on CNN's iReport website with a photo of Gandolfini's arm around his shoulder. Both men are smiling ear to ear.
They exchanged telephone numbers and spent some of their evenings sitting around together on a deck by a lake smoking cigars and telling stories.
"It was like we had been friends forever," Tantalo said.
IReporter Shana O'Neil met Gandolfini when he was shooting in her office in 1994. She remembers him as "Jersey through and through," a trait he did share with mobster Tony Soprano.
But he was so much friendlier, O'Neil said. "I just always think of him as that guy."
His "Sopranos" fame, she said, changed nothing about the way she remembers him.