Chuck Lorre, the creator of The Big Bang Theory, initially had different plans for the show that could have drastically altered its success. The original pilot did not include Penny at all, and a character named Katie was supposed to serve as a darker version of her but did not sit well with networks.
Also, the original plan was to have Katie live with Sheldon and Leonard after being dumped by her married boyfriend. Gilda, another character from the original pilot, was written out, laying the groundwork for Amy's later arrival. Chuck Lorre wanted Leonard and Sheldon to have another roommate, but thankfully he found a winning formula and crafted a hit series.
