The Big Bang Theory almost passed on Jim Parsons as Sheldon Cooper because he was too good during his initial audition. As one of the two original characters who were kept in The Big Bang Theory after its pilot was re-written (the other being Leonard), Sheldon was integral to the show's overall success. Similarly, Parsons proved invaluable with his award-winning work as the character.
At the end of its run, The Big Bang Theory remained a hit ratings-wise for CBS, which is why many were surprised when the show ended after 12 seasons. The cancelation was due to Parsons' decision to leave the sitcom. Instead of moving forward without its most popular character, the choice was made to end the series altogether. This proved how significant Sheldon's role was in The Big Bang Theory, as well as the way Parsons brought the character to life.
However, the popular sitcom wasn't set on casting the actor right away as Sheldon. According to co-creator Bill Prady during a recent appearance on the podcast At Home with the Creative Coalition(via People), his partner, Chuck Lorre, thought Parsons was too perfect during his audition, leading to skepticism he could actually deliver that kind of performance consistently. That was easily solved when Parsons returned for another The Big Bang Theory audition the next day and still hit it out of the park:
We saw — oh God, I don't know, 100 people? And when Jim Parsons came in, he was Sheldon on a level — you know, there were people who came in and you went, 'Okay, well, he's kind of okay,' 'Oh, he's pretty good,' 'Maybe he's the guy.' And Jim came in and he was just — from that audition, he was the Sheldon that you saw on television.
He created that character at that audition. And he left the room and I turned and I went, 'That's the guy! That's the guy! That's the guy!' And Chuck turned and he said, 'Nah, he's gonna break your heart. He'll never give you that performance again.'
I have to say, in the story of my relationship with Chuck, the number of times that I'm right and Chuck is wrong may be... I'm gonna go with one. This may be the only example of where I actually was right. And Jim Parsons came back in the next day and gave us that exact same performance again. It was like, 'This is Sheldon.'
Before Lorre and Prady conducted auditions for Sheldon, the role was previously offered to Johnny Galecki, but he refused, wanting to play Leonard in The Big Bang Theory instead. That opened up the chance for Parsons to come in, and in hindsight, everything worked out for the best since both actors were perfect for their respective roles. Not only that, but they also had incredible chemistry as Leonard and Sheldon, which was integral considering their relationship is one of, if not the main, pillars of the sitcom. If their dynamic didn't work out, the show wouldn't have achieved the incredible success it did.
While The Big Bang Theory has ended, its universe continues to thrive through Young Sheldon. The spin-off prequel series shows the enduring appeal of Parsons' character in particular, as well as his performance, wonderfully emulated by Iain Armitage. It's hard to believe Parsons nearly missed the chance to play his career-defining role, but luckily everything worked out in the end.
Source: At Home with the Creative Coalition (via People)