**Billy Bob Thornton's Unexpected Cameo on The Big Bang Theory**

Throughout its 12 season run, The Big Bang Theory had several memorable guest-stars.

Among the very top of that list includes Billy Bob Thornton. In the following, we're going to take a look at how his unlikely cameo took place, and what got him on the sitcom's radar.

**Billy Bob Thornton's Condition for Appearing on the Show**

Billy Bob Thornton's Statement About His Mother Loving The Big Bang Theory Got Him On The Show

Looking at his resume, few could've predicted Billy Bob Thornton's appearance on The Big Bang Theory. The way it came about was completely random. During a red carpet interview, the actor revealed that The Big Bang Theory was his mom's favorite show.

This prompted Chuck Lorre to reach out, in an attempt to secure the actor for a cameo.

Billy Bob Thornton recalls, "I said in an interview that my mom’s favorite show was The Big Bang Theory. So [exec producer] Chuck Lorre got a hold of my manager and said, ‘Would you consider doing a guest spot for your mom?' And I said absolutely, because I’ll do anything for my mom."

Of course, keeping such a debut a secret is not easy task. Steve Molaro revealed alongside The Hollywood Reporter that the plan was to keep his cameo a secret, and not to promote it.

However, given that the episode was shot in front of 200 fans, that was a daunting task to keep it a secret. Nonetheless, it appears as though things worked out.

Molaro reveals, "We shot it with the audience. We knew that as far as the promos go, they were going to keep a lid on it but we figured we couldn’t control these 200 people in the [taping] audience, it’s probably going to get out somehow. But people managed to keep a lid on it long enough that it was a genuine surprise for a lot of people.

I’m glad it worked out that way. The response seems to be overwhelmingly positive."

**Billy Bob Thornton's Storyline Pitch for a Romance with Penny**

Showrunner Steve Molaro Revealed Billy Bob Made A Storyline Pitch For A Romance Alongside Penny

The actor did have an idea for his Big Bang Theory appearance. It is said that Thornton wanted to play a brief love interest of Penny.

Although the fans didn't get that full experience, Steve Molaro revealed that got a snipped of it as Lorvis made a brief attempt at wooing Penny.

"It did come up a little bit, but he basically got to try to," Molaro revealed about Thornton's request.

Molaro continues, "The idea that came up of Penny taking her engagement ring off while she’s working had been floating around for a while. We thought, what if Billy is this socially awkward, sympathetic doctor who doesn’t quite know how to process Penny’s flirtations with him.

We had that basic idea and went to Billy and his people ran it by them. Billy was on the phone, and he thought it was a really fun idea and was into it. That’s how it began."

Ultimately, the actor had a great experience on the show, while Lorre and company revealed that the door was open for a return, but that it wouldn't be easy given the actor's schedule at the time.

**The Challenge of Keeping Thornton's Cameo a Secret**

Of course, keeping such a debut a secret is not easy task. Steve Molaro revealed alongside The Hollywood Reporter that the plan was to keep his cameo a secret, and not to promote it. However, given that the episode was shot in front of 200 fans, that was a daunting task to keep it a secret. Nonetheless, it appears as though things worked out.

Molaro reveals, "We shot it with the audience. We knew that as far as the promos go, they were going to keep a lid on it but we figured we couldn’t control these 200 people in the [taping] audience, it’s probably going to get out somehow.

But people managed to keep a lid on it long enough that it was a genuine surprise for a lot of people. I’m glad it worked out that way. The response seems to be overwhelmingly positive."

**William Shatner's Initial Reluctance and Change of Heart**

Billy Bob Thornton Wasn't The Only Guest-Star To Make A Pitch About Working Alongside Kaley Cuoco On The Big Bang Theory

William Shatner was another iconic guest-star. However, it took the actor years to finally appear on the show. Shatner revealed that he initially turned down the sitcom given that he wasn't a fan of what creative had for him at the time.

"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,'" Shatner said. "They may have taken umbrage at that, I’m not sure."

So what changed? Well, it was apparently his willingness to work alongside Kaley Cuoco after the two hit it off during a commercial.

"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," showrunner Steve Holland reveals.

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

Clearly, Cuoco was a major presence behind the scenes on The Big Bang Theory.