Watching the full, unaired Big Bang Theory pilot is actually really interesting in terms of seeing what could have been. But the central relationship between Sheldon and Leonard was spot on from the very start.
The unaired pilot of 'The Big Bang Theory' originally featured a central female character named Katie, a tough, street-smart woman played by Amanda Walsh.
This was scrapped after test audiences felt she was too mean to Sheldon and Leonard, leading to the introduction of Penny.