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THEN & NOW: The cast of 'The Big Bang Theory'

INSIDER Logo By Madison Vanderberg of INSIDER | Slide 2 of 17:  When Kaley Cuoco first joined "The Big Bang Theory" as Penny, she was most notable for her role as Bridget Hennessy on the short-lived ABC sitcom "8 Simple Rules."

Kaley Cuoco, who plays Penny, came to "TBBT" with sitcom experience.

When Kaley Cuoco first joined "The Big Bang Theory" as Penny, she was most notable for her role as Bridget Hennessy on the short-lived ABC sitcom "8 Simple Rules."

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