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!
Parsons first credited TV role was in 2002 on an episode of Ed, while his first movie role was as Tim on Garden State. He most recently starred on HBO's The Normal Heart and earned an Emmy nomination. He's won four Emmys for his portrayal of Sheldon Cooper.
Galecki's first role was on a TV movie, Time Out for Dad in 1987. He followed that up with small roles on several movies, before getting back into television. He played Danny Nash on American Dreamer and David MacGregor on Billy before getting his first well-known role on the comedy, Roseanne.
Cuoco-Sweeting's first role was on a TV movie, Quicksand: No Escape in 1992. She also played a young Angela on My So Called Life. Her big break came as Bridget Hennessy on
8 Simple Rules, which she followed up as Billie Jenkins on Charmed.
Bialik's first role was on the original Beauty and the Beast playing a young girl, Ellie. She went on to be cast on some of the best shows of the day, including Facts of Life, Webster, and MacGyver. In 1990, she took on the titular role of Blossom Russo on Blossom. She joined The Big Bang Theory in Season 3 as Amy.