The Big Bang Theory: The Vampire Diaries Star Who Was Almost The Pre-Penny Lead

"The Big Bang Theory" ran for so long on CBS that it's hard to believe the beloved sitcom almost didn't make it to air. But before it was a 12-season success story, the show was just another pilot scrapped by network executives — and for good reason. Jessica Radloff reports (via Yahoo) in her book, "The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series," that according to show co-creator Chuck Lorre, the pilot filmed for CBS' 2006-07 season "didn't really understand the characters yet." One of those characters never made it to air: Katie, the pre-Penny lead, who was initially portrayed by "The Vampire Diaries" star Jodi Lyn O'Keefe, and later by Canadian actor Amanda Walsh.

The character of Katie was written as a cosmetic salesperson at a department store with a tough exterior and vulnerable interior. In the original, unaired pilot, Katie meets Sheldon and Leonard after a breakup with her boyfriend leaves her homeless. With nowhere else to go, she moves in with the boys, but a miscommunication with Leonard causes her to move out — and later, back in again. Although she was the first actor cast in the role, O'Keefe's time as Katie was short-lived. During the show's first table read, Jim Parsons thought she nailed what was in the script, but the show's creators disagreed. They thought her performance was too harsh and dark and they fired O'Keefe before filming on the pilot began.

In her book on "The Big Bang Theory," Jessica Radloff wrote that aside from O'Keefe, three actors were also considered for the role of Katie: Marisa Tomei, Tara Reid, and Elizabeth Berkley — who co-creator Bill Prady described as "terrific." After O'Keefe was fired, production only had three days to recast the part, so they brought in Amanda Walsh from the ABC dramedy "Sons and Daughters." Walsh had previously auditioned but wasn't hired during the first round of casting. However, she ended up landing and filming the role.

As it turned out, the issue with Katie didn't lie solely within the person portraying her. When responding to the pilot, audiences took issue with the way the character was written and struggled with the mean and mocking way she treated Sheldon and Leonard.

In the year after the original pilot and before the actual first episode of "The Big Bang Theory," the show's creators went back to the drawing board and transformed the role of Katie into the character of Penny, as played by Kaley Cuoco. Cuoco auditioned for the role of Katie as a 20-year-old, and while the creators loved her performance, they felt she was too young for the part, and that her optimistic energy didn't fit with what they envisioned for the character. After Katie was rewritten as Penny, a sweet, caring, bubbly Midwesterner, Cuoco auditioned again and this time, she landed the role.