Some of the actors in the cast of "Big Bang Theory" are Johnny Galecki, Jim Parsons, Kaley Cuoco-Sweeting, Kunal Nayyar and Simon Helberg. Some others are Melissa Rauch, Mayim Bialik, Sara Gilbert and Laurie Metcalf.
Johnny Galecki plays Leonard Hofstadter, an overachieving experimental physicist at CalTech University. Jim Parsons plays Leonard's roommate, Sheldon Cooper, a fellow CalTech physicist who is both brilliant and highly anti-social. Kaley Cuoco-Sweeting is cast as Penny, an aspiring actress who lives across the hall. She is also the on-and-off love interest of Leonard. Kunal Nayyar plays Raj, friend of the group and CalTech astrophysicist, and Simon Helberg plays friend Howard Wolowitz, an aerospace engineer who also works at CalTech.
Melissa Rauch plays Bernadette, a microbiologist and the love interest of Howard. The two characters married in the final episode of the fifth season. Mayim Bialik is cast as Amy Farrah Fowler, Sheldon's smart and quirky girlfriend. Sara Gilbert guest stars as recurring character Leslie Winkle, who casually dates Leonard. Laurie Metcalf also has a recurring role on the show. She plays Mary Cooper, Sheldon's devoutly religious Texan mother. Galecki, Metcalf and Gilbert all also starred in the long-running sitcom "Roseanne," which was popular in the early 1980s and through much of the 1990s.