THEN & NOW: 'Big Bang Theory' Stars Before They Were Famous

It all started with the Big Bang — or did it?

Fans of CBS' Emmy-winning sitcom The Big Bang Theory have come to know and love Kaley Cuoco, Johnny Galecki, and Jim Parsons as their characters, Penny, Leonard, and Sheldon.

But they — and the rest of their adorably geeky gang — were hard at work in Hollywood long before the show's meteoric success.

Here's a look at the cast of The Big Bang Theory in some of their most noteworthy early roles.

"Big Bang Theory" cast then & now >

THEN: After appearing as Brady Bunch actress Maureen McCormick in the 2000 TV movie "Growing Up Brady," Kaley Cuoco scored a starring role on the ABC sitcom "8 Simple Rules for Dating My Teenage Daughter" (later known as "8 Simple Rules").

Then just 16 years old, she played Bridget Hennessy, the beautiful but ditzy oldest daughter of Paul Hennessy (the late John Ritter, who died three episodes into the second season). The series was canceled due to low ratings in 2005.

NOW: As Penny on "The Big Bang Theory," Cuoco has won one Critics' Choice Award and been nominated for multiple People's Choice and Teen Choice Awards.

(Not to mention the many accolades given to the cast and crew as a whole.) According to Deadline, she earns $350,000 per episode -- and is looking to top that if the show is renewed for an eighth season next year.

THEN: Before finding his inner geek on "The Big Bang Theory," Johnny Galecki was best known for playing David Healy on "Roseanne."

But he also had roles in some other 1980s and '90s classics. In 1989, at age 14, he starred as Rusty Griswold in "National Lampoon's Christmas Vacation," alongside Chevy Chase, Beverly D'Angelo, and Juliette Lewis.

(Above photo is from "Roseanne")