Kaley Cuoco was a major reason for the success of The Big Bang Theory. Despite her brilliance on the show, the actress typically watched herself on mute... given she couldn't stand listening to her own voice.

Since the show, but in truth, fans will never forget her time on the sitcom.

Not only did she thrive on-screen, but she was also very instrumental behind the scenes. Let's take a look which guest-star she played a major hand in getting onboard during the final season.

William Shatner Turned Down The Big Bang Theory

has some iconic guest-stars over its 12 season run, including the likes of Bill Gates, Elon Musk and Stephen Hawking.

However, surprisingly, not every person was as excited to work on the show. During the early stages when it was just a script, Macaulay Culkin turned down a lucrative offer to appear on the sitcom as a regular.

In addition, a certain guest-star initially said no to the sitcom, given that he felt as though there was a lack of direction for his character. Although William Shatner would eventually reconsider down the road,

The icon stated, "I've had several conversations with the creators, and what they wanted me to do, didn't seem to be exactly right, so I said 'find something that's better'. They may have taken umbrage at that, I'm not sure... They wanted me to play myself a little obliquely, and they said it would work out, but I needed more assurance on that."

During the last season, Shatner was finally brought into the mix and a major reason for it happen to be Kaley Cuoco.

Years Later William Shatner Reconsidered Because Of His Friendship With Kaley Cuoco

Shatner finally appeared during season 12, episode 16, . The guest-star lineup was a stacked one, featuring the likes of Kareem Abdul-Jabbar, Joe Manganiello and Kevin Smith.

Producer and Showrunner Steve Holland opened up, . According to Holland, the show had a big list of guest-stars for the final season and Shatner was at the very top of the list.

So what changed this time? Well, it seems like Shatner's relationship with Kaley Cuoco played a major role, as the two worked alongside one another in a commercial. Shatner even requested shooting a scene with Cuoco during the early stages.

“So we reached out to him again,” he says. “I got on the phone and chatted with him about what we were thinking about for the episode — at that point we didn’t have a script — but I think he felt like he wanted to be a part of this before it came to an end."

“I think what changed going into the final season is that he knows [series co-star] Kaley [Cuoco] from doing [Priceline] commercials together and they’re friendly."

“When I got on the phone, one of the things he asked was, ‘Will I get to play a scene with Kaley?"

Not only was it a great cameo, but the cast was impressed by Shatner's work during his brief time on the show.

How Was William Shatner Received Behind The Scenes By The Cast And Crew?

Holland and the cast loved to see Shatner's process during his time on the show. It is said that William was quite the pro, and took a couple of takes to really perfect his role on the sitcom.

“He would play a scene for a couple of takes until he found a delivery he liked and then really locked into it. He’d play around with a line a little bit and find what felt right to him and lock into that."

“He was nothing but receptive,” Holland says. “He’s made fun of his persona over the years, but if he’s doing something, he wants it to be different from what he’s done before. When we were first chatting, one of the things he thought was funny was if [in the episode] he was really into the [Dungeons & Dragons] game — so anytime someone would go ‘Let’s go,’ he’d say, ‘C’mon, guys, let’s get back. We’re playing Dungeons & Dragons here!"

It took a minute to get him onboard but ultimately, everything worked out for William Shatner.