Bob Newhart turned out to be one of the best guest stars on . He thrived in the role, but as we'll reveal in the following, he did have a couple of prerequisites prior to joining the cast, and Chuck Lorre ensured they were all going to be met.

Newhart was the perfect fit as Professor Proton, and that held true for his dynamic alongside Sheldon, aka . In the following, we're going to also take a closer look at their relationship, and how the two felt about Professor Proton's death. Jim wasn't exactly thrilled, while both agreed it was handled perfectly by the show.

Let's take a closer look along with so much more pertaining to Newhart's time on the series.

Bob Newhart Had Two Conditions To Joining The Big Bang Theory

Bob Newhart admitted that his relationship with Chuck Lorre, the creator of goes way back. Speaking alongside , and finally proved to be the perfect fit.

"Chuck was on the lot when we were doing and at lunch, he’d come to our stage and sit there. We’ve been going back and forth, and we never could find a project that we could both agree on until ."

As for agreeing to be on the show, Lorre and Newhart agreed that two conditions needed to met, which included Newhart reappearing on the show as a somewhat regular, along with Newhart shooting his scenes if in front of a live audience.

The actor revealed, "My scenes had to be taped live. There’s a tendency to pre-tape a lot of stuff and put a laugh track on it and you lose something. With , , , and it was always done in front of live audience. I always felt that the live audience gives it adrenaline. That’s the only way I function. No. 2, I wanted it to be a semi-recurring role."

Newhart got both of his requests and he turned into one of the best recurring guest stars on the show. Even when he passed away on the show, Bob continued to appear.

Jim Parsons Could Not Understand Why Bob Newhart Was Killed Off, But Appreciated His Spirit Manifestation

Jim Parsons and Bob Newhart took part in a Q&A together for . During the conversation, the two spoke about the first time they met. Newhart revealed it took place at the while Jim didn't recall the moment given all the chaos that usually takes place at such events.

Nonetheless, Parsons had a blast with Newhart on the show, but just couldn't understand as to why his character of Professor Proton was killed off. .

"I asked him if he had asked for a raise. Because why else would you kill off Mr. Newhart’s performance on our show?"

However, Parsons added that he appreciated the spirit manifestation twist, "But this spirit manifestation they’ve opened up now is great," he said at the time.

Newhart would also reveal that he was fine with the moment, especially given how touching it all turned out to be.

"I think it was (producer) Steve Molaro’s idea. He ran it by me and I said, “That sounds great.” The scene was funny anyway when we shot it in front of the audience, but the special effects heightened the comedy even more. And I thought it was very touching."

Newhart ultimately had a blast with his time on the series.

Bob Newhart's Experience On The Big Bang Theory Exceeded His Expectations

Looking back at his experience on Newhart calls it nothing but a positive. In addition, the actor wasn't surprised that the ratings continued to soar, while other shows at the time were struggling with ratings. Newhart applauded the cast and the writing in particular.

"It’s beautifully cast, has great writing and it’s intelligent. There was a longing for something intelligent — to credit the audience being intelligent. It doesn’t talk down to the audience at all."

Newhart did admit that his take to comedy did adjust during the show, given the way sitcoms have changed over time.

"There’s a rhythm with setting up jokes, which the audience wanted. I don’t know which came first — if the producers and writers decided that was way to go and audience went along with it or if audience wanted it to go that way and producers and writers realized it. Obviously, it’s changed in terms of the material you can deal with."

In the end, it all worked out for best.