Sheldon (Jim Parsons) is an accomplished Caltech theoretical physicist from Texas with an I.Q. of 187. He speaks fluent Klingon, is unable to discern sarcasm, and claims to be the perfect human specimen.
Leonard Hofstadter
Leonard (Johnny Galecki) is an experimental physicist from New Jersey. He received a Ph.D from Princeton University at age 24. He owns several Star Wars hygiene products and a Battlestar Galactica colonial warrior flight suit. He is lactose intolerant.
Penny
Penny (Kaley Cuoco) is a waitress at The Cheesecake Factory. She was raised in Omaha, Nebraska. She is disorganized, a terrible driver, snores loudly, and has had several run-ins with the law. She’s also a vegetarian but loves eating steak.
Howard Wolowitz
Howard (Simon Helberg) is 27 years old and lives with his mom. He is the only geek in the group who does not have a Ph.D. He invented the zero-gravity human-waste disposal system (a.k.a. the "space toilet"). He has an extensive belt collection and a passion for turtlenecks.
Rajesh Koothrappali
Raj (Kunal Nayyar) is an accomplished astrophysicist and was once named to People Magazine's "30 Under 30" to watch list. He is originally from New Delhi, India but despises Indian food. He also suffers from selective mutism.
Amy Farrah Fowler
Amy (Mayim Bialik) is a neurobiologist who once online dated herself in exchange for her mother's George Foreman grill. She is prone to night terrors, gets constipated by travel, and successfully taught a monkey to smoke cigarettes.
Bernadette Rostenkowski
Bernadette (Melissa Rauch) worked with Penny at the Cheesecake Factory but now is a microbiologist. She is (usually) dating Howard. She hates puppies, children, magic, and is self conscious about her height.