The Big Bang Theory is an American sitcom created by Chuck Lorre and Bill Prady, both of whom serve as executive producers on the show, along with Steven Molaro. All three also serve as head writers. It premiered on CBS on September 24, 2007.
The show is centered on five characters: roommates Leonard Hofstadter and Sheldon Cooper; Penny, a waitress and aspiring actress who lives across the hall; and Leonard and Sheldon's equally geeky and socially awkward friends and co-workers, aerospace engineer Howard Wolowitz and astrophysicist Raj Koothrappali. The geekiness and intellect of the four guys is contrasted for comic effect with Penny's social skills and common sense.
Over time, supporting characters have been promoted to starring roles: Leslie Winkle, a physicist colleague at Caltech and, at different times, a lover of both Leonard and Howard; Bernadette Rostenkowski, Howard's girlfriend (later his wife), a microbiologist and former part-time waitress alongside Penny; Stuart Bloom, the cash-strapped owner of the comic book store the characters often visit, and neuroscientist Amy Farrah Fowler, who joins the group after surreptitiously being matched to Sheldon on a dating website.
From Wikipedia: http://en.wikipedia.org/wiki/The_big_bang_theory