The Real Reason Billy Bob Thornton Agreed To Appear In The Big Bang Theory

When a sitcom runs for upwards of 10 seasons or more, showrunners and their writing staffs have to get creative to keep things fresh (as any faithful "Cheers" fan could tell you). Actually, that's not entirely true. Depending on the audience, sometimes an endless string of celebrity cameos is enough to keep folks tuning in long after the novelty of the original hook has worn off.

It's probably not fair to say that a show as beloved as "The Big Bang Theory" relied heavily on splashy cameos to remain buzzworthy (after all, the series just barely launched its second spinoff in "Georgie & Mandy's First Marriage" at the time of writing), but the rate at which the sitcom deployed them felt a tad shameless. Some of the one-and-done guest appearances made sense for the geek-skewing show — e.g. Mark Hamill, James Earl Jones, and Leonard Nimoy were natural fits. On the other hand, "Big Bang Theory" guests like Jessica Walter, June Squibb, and Billy Bob Thornton seemed to come out of nowhere.

Thornton felt especially odd because his cameo wasn't promoted. He just randomly turned up, leaving viewers both delighted and puzzled. Thornton's an appealing presence, but he's not exactly known for his geek cred.

So, why did he turn up on "The Big Bang Theory?" Because he really, really wanted to.

In a 2014 chat with Entertainment Weekly, showrunner Steve Molaro said he discovered Thornton was a fan of "The Big Bang Theory" while watching an interview on television. "He was saying how much he likes 'Big Bang Theory,' and watches it all the time, and gets so into it [that] he starts talking to the characters on the screen." That's an unusual level of attachment, so of course they wanted him talking to their characters inside the screen (technically, behind the camera; the people who appear inside your television screen do not live there).

The producers thought the "Sling Blade" writer-director-star would be perfect for an episode titled "The Misinterpretation Agitation," in which Penny (Kaley Cuoco) accidentally initiates an awkward entanglement while performing her duties as a pharmaceutical rep. According to Molaro:

"When we started thinking about Billy Bob, the thought was that he could be the doctor who doesn't quite understand the signals — that this would be a socially awkward doctor who falls for Penny's sales flirtations. We went back to Billy and his people with that thought, and they thought it was really fun and cool, so we went from there."

Thornton's guest spot turned the episode into a winner with audiences, who were caught completely by surprise when Thornton showed up. As Molaro noted, "We knew that the network wasn't going to promote it [...] but somehow it stayed a secret." So, if you're looking to ding "The Big Bang Theory" for getting too cameo happy later in its run, look elsewhere!