Kaley Cuoco, Jim Parsons and Bob Newhart Kaley Cuoco, Jim Parsons and Bob Newhart

Bob Newhart, 83, often turns down requests to guest star on sitcoms, so kudos to CBS's The Big Bang Theory for landing him on its May 2 episode. Exec producer Chuck Lorre asked him what it would take to do one of his shows and, Newhart says, "I specified Big Bang because of the writing and the live audience."

He plays Professor Proton, the former host of a kiddie science show. "Sheldon and Leonard watched it religiously, and it influenced them to go into science," Newhart says. "When they find out he's doing appearances, they book an appointment." Tailored to Newhart's dry wit, the professor is incredulous of the adoration but plays along for the payday. And he may be back. The last scene "sets it up for me to return a couple more times next season."

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