When speaking to Entertainment Weekly, the cast was asked about their first impressions of each other. Kaley Cuoco talked about how she knew right away how Jim Parsons was the perfect actor to play Sheldon.
"At the audition I saw Jim sitting there by himself, and we were the only two there," she said. "He was very quiet and had a BlackBerry in his hand, playing with it. He looks at me and said, 'You don't know how to work this thing, do you? I just got it.' He was very cute how he said it. I thought he could totally play Sheldon. Charming and innocent."
According to creators Bill Prady and Chuck Lorre, Cuoco's character was a major factor in Sheldon breaking out of his shell.
"Jim Parsons' speech about why he sits in that particular spot on the couch in the pilot episode," Lorre said when asked his favorite moment in the show. "I think we all watched that and understood something remarkable was happening. There were no real jokes in the speech, it was just a worldview that was so precise, and he brought it to life. It was an astounding moment I'll never forget."
"I love the episode where Sheldon doesn't like that Leonard is dating Raj's sister," Prady said. "She was a lawyer and kept finding loopholes in the roommate agreement and was using it against him. Sheldon gets so mad that he ends up threatening to tell her parents she was dating Leonard and uses the Star Trek self-destruct sequence to do it."
He continued, "To me, that was this great nerd explosion. Then there's the incredible moment with the Christmas gift where Penny gives Sheldon a napkin with Leonard Nimoy's DNA on it."
Lorre added, "That's when he hugged Penny. It was the first time he laid a hand on her. That was a big character breakthrough moment, he was so alienated up to that point."
Galecki told Entertainment Weekly that Cuoco made quite an impression on the rest of the cast in the beginning. He revealed that everyone thought she was the coolest person on the show.
"We all thought Kaley was the coolest person in the cast," Galecki said. "As soon as we were done with rehearsals or the live audience, she was like taillights. We all assumed she had much better social plans than we did. Maybe a year in, she started spending more time with us offstage and confessed she had nowhere to go. She was maybe going to ride her horses, probably."
Galecki also said that he expected Cuoco to have friends outside the show and was shocked when she started hanging out with them.
"We all thought Kaley was so social and must have had so many friends," he said, before directly speaking to Cuoco. "You just beelined out of here. We used to hang out afterward. Then you finally came and said, 'I don't have any friends. Can I hang out with you?'"
"Well, you never invited me to hang out after!" Cuoco said.
"Because we thought you were hipper than you are!" Galecki responded.
Jessica Radloff's book "The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series" detailed a ton of juicy behind-the-scenes secrets. Part of the book delved into the tension on-set when the rest of the cast discovered Parsons would be leaving the show. According to the book, Johnny Galecki said the news was shocking because Parsons didn't tell the cast he planned to leave prior to them discovering the show was canceled.
"I just disagreed with how it was handled," Galecki said. "We thought we were going into [co-creator] Chuck [Lorre]'s office to talk about renegotiating, and then Chuck tossed the baton to Jim. And Jim was shocked and obviously caught off-guard."
There was also indications that Cuoco and Parsons weren't getting along too well in light of the announcement.
"Kaley could barely make eye contact with Jim during the run-through," executive producer Steve Holland said.
He added, "At the time, there were a lot of hard feelings between Parsons, and Galecki and Cuoco, who weren't privy to everything that had unfolded leading up to the decision to end the show with season 12, or unaware why they weren't brought into the fold sooner. Understandably, the next day at work — which was a Thursday run-through — was fraught with tension."
CBS was reportedly preparing to renew The Big Bang Theory for another two seasons. However, when Parsons announced his desire to leave the show, the network didn't think there would be enough of a story to tell. The character of Sheldon was a big part of the show, so it was decided that it would be canceled.