Jon Basso said John Alleman, whose "Patient John" caricature is on the high-calorie eatery's menus, suffered an apparent heart attack at a bus stop last week and was taken off life support Monday, the Las Vegas Sun reported Tuesday.
Alleman, who was a daily fixture at the restaurant but was not on the payroll, was 52 years old.
"He lived a very full life," Basso said. "He will be missed."
"He never missed a day, even on Christmas," Basso said. "People just loved him. He connected with people in a real way."
Alleman is the second unofficial spokesman to die since the restaurant opened two years ago. In March 2011, Blair River, a 29-year-old who weighed 575 pounds, died of flu-related pneumonia.
Basso said the restaurant has no plans to change its menu, which includes a world record-breaking 9,982-calorie, 3-pound Quadruple Bypass Burger.
"The grill is where you can be yourself. We accept people as they are," Basso said. "[Alleman's death] isn't going to stop us from what we're doing. People have got to live their lives."
Basso said Alleman, who only weighed 180 pounds at the time of his death, should serve as a warning that heart attacks can strike anyone.
"Heart attacks aren't a laughing matter," he said. "You don't have to be tremendously old or fat. You can be in your 30s and 40s and die of a heart attack."