The Big Bang Theory is a huge hit. It's already been renewed for three more seasons, which will put it through season 10.
When the series began, only two of the five lead actors had ever been on a successful show that ran for multiple seasons. Johnny Galecki played Darlene's boyfriend on the successful Roseanne for several years and Kaley Cuoco-Sweeting was best known as Bridget Hennessey on 8 Simple Rules.
In Season 3, Blossom's Mayim Balik and Melissa Rauch joined the show adding more laughs and romance to the comedy.
Before The Big Bang Theory cast played scientists and a waitress (technically, Bernadette was both), they played an wide range of characters. Who was on Joey? MacGyver? Charmed?
Check out each of their first credited roles and other highlights!
Need to catch up before The Big Bang Theory Season 8 begins? Watch The Big Bang Theory online now!