The Big Bang Theory is an american sitcom (short for the term "situation comedy"), created by Chuck Lorre and Bill Prady.
The creators of the programme mentioned that, what makes the production of The Big bang Theory easier, is the fact that when the characters are created, the script almost writes itself, especially with Sheldon, played by Jim Parsons, due to his distinct use of vocabulary.
After a few series were aired, both in the UK, and the US, the creators received a lot of fan mail, pressuring their own ideas towards the creators.
Funnily enough, the creators of the show have not yet planned or written how