Leslie works at Caltech with Leonard as a physicist. Leslie is a female carbon copy of Leonard, even dressing similarly in hoodie sweatshirts and black-framed glasses. In season 1, Leonard asked her out instead of Penny because he felt like Penny was too good of a catch for him.
Sheldon disapproves of their relationship, causing ongoing tension between the two. Ultimately, Leslie and Howard form a casual, no-strings-attached relationship, with Howard having emotional feelings towards her.
Jim Parsons as Sheldon Cooper – Then
Sheldon has been a fan favorite since the start of the show. He is a Caltech theoretical physicist and was once roommates with Leonard, his best friend. He easily annoys those around him, has a very serious demeanor, and is anal about his routine.
He rocks his geekiness and his arrogance, believing himself to be perfect. He started dating neurobiologist Amy in season 5, and they become engaged in season 10.
Jim Parsons as Sheldon Cooper – Now
Jim is another star of the show who found himself blossoming in his role as the beloved Sheldon. He has taken home a Golden Globe and an Emmy for his work.
You may have recognized his voice in the animated movie "Home," where he plays an eccentric and freethinking alien named Oh. Jim made $900,000 per episode (along with John and Kaley), making him one of the highest-paid actors in comedy television.
Sara Gilbert as Leslie Winkle – Now
Sara was and still is best known for her long-time role as Darlene Conner on "Roseanne." The actress now has 3 children and is married to Linda Perry.
"The Conners," a spinoff of "Roseanne," aired in 2018. The "Roseanne" reboot was canceled following a controversial tweet by star and executive producer Roseanne Barr.
Mayim Bialik as Amy Fowler – Then
Amy started on the show during the season 3 finale, where she meets Sheldon. Raj and Howard found her on a dating site and figured that this neurobiologist would be a great fit for Sheldon.
The two date until becoming engaged (with a short break in between) in season 10. Amy is also in Penny’s posse with Penny and Bernadette.