'Big Bang Theory': Bob Newhart, Regina King & More Bangin' Guest Stars (PHOTOS)

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The Proton Resurgence
Michael Yarish/Warner Bros.
THE BIG BANG THEORY
CBS

Bob Newhart

“He was wonderfully written,” Newhart says of Arthur Jeffries, aka kids’ science-show host Professor Proton. After Arthur’s passing, he often appeared to Sheldon via dreams to offer advice.

THE BIG BANG THEORY
CBS

Regina King

Janine Davis, a human resources administrator at Caltech, where the guys work, is “more of a straight face,” says the Oscar winner, who adds that being part of the show “makes my heart giggle.”

THE BIG BANG THEORY
CBS

Stephen Hawking

One of the guys’ heroes, the cosmologist first appeared as himself in Season 5. (He returned six times!) “Everyone was in awe,” recalls Galecki. Adds Kaley Cuoco, “You could tell he loved being there.”

THE BIG BANG THEORY
CBS

Christine Baranski

Of her favorite moments as Beverly, Leonard’s frosty psychiatrist mother, Baranski lists “singing rock with Sheldon, getting drunk with Penny and expressing anything maternal with Leonard.”

THE BIG BANG THEORY
CBS

Laurie Metcalf

Jim Parsons was starstruck by Metcalf when she debuted as Sheldon’s religious and overbearing mom, Mary, in Season 1. “I was so frightened I would expose myself as a fraud [of an actor],” he says.

THE BIG BANG THEORY
CBS

Sara Gilbert

Leslie Winkle, Leonard’s snarky ex-girlfriend, “could talk down to [the guys] and the audience didn’t think less of her,” says Johnny Galecki. “Sara’s one of the few guest stars to pull that off.”

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The Big Bang Theory has had many memorable guest stars over its 12 seasons, but some were really out of this world.

Ahead of the CBS comedy's finale on May 16, the cast has been looking back on the series' beginnings, fandom, catchphrases, and more. And what would TBBT be without the colorful characters (and familiar faces) that stopped by through the years?

Click through the gallery above for our picks of the most iconic guest appearances, from Bob Newhart to Regina King, and hear what the actors had to say about their characters!

The Big Bang Theory, Thursdays, 8/7c, CBS

Johnny Galecki & Kaley Cuoco Get Silly to Celebrate the 'Big Bang Theory's Final Episodes (PHOTOS)See Also

Johnny Galecki & Kaley Cuoco Get Silly to Celebrate the 'Big Bang Theory's Final Episodes (PHOTOS)

The co-stars and on-screen spouses had fun ahead of the show's big farewell.