There Are Two Pilots Of The Big Bang Theory
The Big Bang Theory actually had two pilots made. The first pilot was produced for the 2006 to 2007 television season but it never went to air. The second premiered on September 24 2007.
In the original un-aired pilot, the show’s structure was very different from what we are used to seeing on The Big Bang Theory today. Characters Leonard Hofstadter ( played by Johnny Galecki) and Sheldon Cooper (Jim Parsons) are the only two to appear in both the un-aired pilot and the series.
Before the first episode of The Big Bang Theory appeared on CBS, the pilot episode was available on iTunes for free.