Len Lesser, who is known as Uncle Leo from Seinfeld, died in his sleep from complications of pneumonia in Burbank, California.
Lesser was 88 when he died. His daughter, Michele Lesser, told CNN that his passing was "very peaceful" and that they had hoped for a "quick and painless death."
"He was a great grandpa, and an amazing father. He had a heart of gold -- and a sense of humor of platinum," she said.
In addition to Seinfeld, Lesser was a hard-working actor appearing in more than 500 television, film and stage appearances. He had a recurring role on Everybody Loves Raymond as Garvin, and appeared in hit shows like ER, Mad About You and Thirtysomething. He also served in the Army during World War II.
The cast of Seinfeld has expressed their thoughts on Lesser's passing. "I'll never forget when Uncle Leo was in prison and tattooed 'Jerry Hello' on his knuckles," Jerry Seinfeld told The New York Daily News, adding he was "a very sweet guy" and that they "always loved having him on the show."
Jason Alexander, who played George Costanza on Seinfeld, tweeted his condolences. "Len was a tremendous guy. He was a smart actor/comedian who knew exactly what he was doing in the creation of Uncle Leo. I enjoyed many wonderful conversations with Len who was so openly grateful to be part of our show and so humble about his stunning contribution to it. I am so happy to have known him and my sympathies go to his family. But his was a fun life and he leaves many fans behind and many who will be enjoying his work for years to come."