Comedian and actor Bill Cosby waves to the cameras as he enters the Kennedy Center in to receive the Mark Twain Prize for American Humor in Washington, D.C., on Monday. (Jacquelyn Martin/Associated Press)Chris Rock and Jerry Seinfeld saluted their fellow funny man Bill Cosby with the top U.S. comedy prize Monday night, along with two co-stars from The Cosby Show, Phylicia Rashad and Malcolm-Jamal Warner.

Still, someone had to hold Cosby back to keep him from crawling over a balcony and joining fellow comedians on stage as the stars lined up to pay tribute to his life's work.

When the lights went out for the start of the 12th annual Mark Twain Prize for American Humor, Cosby filled the dark silence Monday night. "Hellooo?" he called out at the John F. Kennedy Center for the Performing Arts in Washington, D.C. And once again, he had his audience laughing.

Cosby quipped that usually when a man sees his life flash before his eyes, it's for a bad reason. "But this is all right," he said.

The comics hailed Cosby's work breaking down racial barriers and stereotypes and replayed his standup routines.

Michelle Obama, wife of U.S. President Barack Obama, and Jill Biden, Vice-President Joe Biden's wife, were among those in Washington watching clips from Cosby's long career — from his classic standup routine of Noah's chat with God about building an ark to dealing with the stresses of raising a family as a TV dad.

Seinfeld and Rock shared the stage and said they followed Cosby's comedy albums as children, which inspired their own careers. Then they got lost in banter about how they could never measure up, after seeing Cosby together more recently at New York's Apollo Theater.

'I'm not that funny'

"What was he wearing?" Rock said.

"Something ridiculous," Seinfeld quipped. "But he did two hours — all new material."

"I'm not that funny," Rock said.

"I'm definitely not that funny," Seinfeld said.

Instead, Seinfeld and Rock tossed to a clip of Cosby's classic impression of a visit to the dentist.

"The first thing he grabs is an iron hook," Cosby says in the clip. "Then he starts to drill and you see and smell smoke coming out of your mouth!"

As a clip of Cosby's famous impression of a visit to a dentist ended, Cosby turned to his wife, Camille, who smiled and clapped. Cosby later said comedians' wives often want autopsies of their husbands' brains to see what's going on in there.

Cosby Show considered ground-breaking

Critics often point out that The Cosby Show, which aired in the 1980s, broke new ground because it was about a successful black family with a father who's a doctor and mother, a lawyer, raising five children.

Comedian Dick Gregory said Cosby started breaking barriers even earlier with the I Spy TV series, which cast a black man and a white man as co-stars. After that, Gregory said, promoters never again referred to him as a "Negro comic."

Of all his accomplishments as a comedian, actor, author and television producer, Cosby said he is most proud of the Cosby Show, which he carefully crafted.

Rashad, who played Claire Huxtable on the series, flew from London where she is in rehearsal for Cat on a Hot Tin Roof to be part of the show at Cosby's request. Warner, who played Theo on the show, said he has been in touch with his TV dad ever since. Now, he said he is far enough removed to watch himself in reruns and said the show is a testament to Cosby's genius.

"He always said in 20 years he wanted the show to still be relevant, and here we are," Warner said.

Cosby, 72, has won other major awards, including the Presidential Medal of Freedom in 2002. Still, the Mark Twain Prize is special, he said, because Twain was the "quintessential American writer — because he held his language and his love for words in perfect American form."

The tribute will air Nov. 4 nationwide on PBS. Cosby insisted the performances at the tribute be free of profanity and that the show reflect his emphasis on education.

"The show is very, very important to me," Cosby said in an interview. "It makes me aware that as a monologist and a writer and a performer, I've done some wonderful work."