Billy Bob Thornton appeared as a guest-star on The Big Bang Theory after revealing in an interview that it was his mom's favorite show. Chuck Lorre reached out and Thornton agreed to a cameo. He also made a pitch about a storyline with Kaley Cuoco's character Penny, which resulted in a small attempt at a romance. William Shatner initially turned down the show but finally appeared in its final season due to his willingness to work alongside Cuoco, with whom he had previously done commercials. Cuoco was a major presence behind the scenes of the sitcom.
