John Pinette has died at the age of 50.
The stand-up comedian, who famously appeared in the final episode of Seinfeld, was found in a hotel room in Pittsburgh, Pennsylvania. He had died of natural causes.
John had just started a tour across the US and Canada which was due to end in June.
He was known for making self-deprecating jokes about his weight during his comedy shows, which had titles including I'm Starvin'! and Still Hungry.
Agent Nick Nucifero told US media that John had been working on a stand-up project when he died.
"He should be celebrated for the amazing comedian he was," he said.
In the final episode of Seinfeld, John starred as an overweight man carjacked at gunpoint.
The show's stars stand by and make fun of him before they are arrested for violating the 'Good Samaritan Law'.