Mark Hamill, the Star Wars legend, agreed to make a cameo appearance on The Big Bang Theory without even reading a script. Showrunner Steve Holland revealed that when they were planning the wedding episode, Hamill was the first name on their list of dream guest stars. Initially hesitant due to the lack of a script or clear idea, Hamill decided to take a leap of faith and trust the show's creators.

Hamill spent a few hours talking to the writers and hanging out with them before making his decision. Despite not knowing the specifics of his role, he signed on without seeing a single word. Holland described Hamill as a class act, generous with his time, and open to whatever the show had in store for him.

He was genuinely nice, happy to take selfies with people, and chat with them. From a professional standpoint, Hamill had his own ideas but was willing to try anything the show asked of him. Holland considered working with Hamill a dream come true, praising his effortless transition into the sitcom genre due to his theater and voice work experience.

In addition to Hamill, another major guest star on The Big Bang Theory was Billy Bob Thornton. He agreed to do a cameo after Chuck Lorre, the executive producer, contacted him upon hearing that Thornton's mom loved the sitcom. Thornton gladly accepted the offer, stating that he would do anything for his mom.

His role on the show was successful, and he even requested a romance storyline with Penny, which was granted. Fans hoped to see more of Thornton on the series in the future.

Overall, Mark Hamill had a positive experience appearing on The Big Bang Theory, despite not having a concrete script beforehand. He trusted the show's creators and enjoyed his time on set. Similarly, Billy Bob Thornton was motivated to do a cameo by his love for his mom and had a satisfying experience playing a role on the popular sitcom.