The Big Bang Theory has managed to feature a wide variety of guest stars over the years, often drawing from the sci-fi sphere. Everybody from Katee Sackhoff of Battlestar Galactica and Wil Wheaton of Star Trek: The Next Generation to Carrie Fisher and James Earl Jones of Star Wars fame have turned up. The show is officially pulling out all the stops for the Season 11 finale on the guest star front. Mark Hamill will appear as a guest star, and he's not the only one.
Mark Hamill--yes, Luke Skywalker himself--will turn up in the Season 11 finale, which will also just so happen to feature the long-awaited wedding of Sheldon and Amy. EW reports that Hamill will be joined on the guest star front by Kathy Bates (who recently signed on to return to TV as a regular), Lauren Lapkus, and the magician Teller (apparently without Penn). There's no news yet of who these actors will be playing or why they'll appear, but we can make some guesses.
The odds are that at least Mark Hamill will play himself on The Big Bang Theory. Since both Carrie Fisher and James Early Jones appeared as themselves in earlier seasons of the show, it would be a stretch if Mark Hamill turned up as Random Wedding Guest #37. The bigger question is of the context for Hamill's appearance. It's entirely possible that one of the guys (or perhaps Penny, who recently brought a big name into the fold) manages to get Hamill to attend the wedding as a glorious present to Sheldon.
It's also possible that Amy has been secretly related to Mark Hamill all along and never mentioned it to Sheldon, wanting him to love her for her rather than for her connection to Luke Skywalker. How funny would it be if Mark Hamill just walked into the wedding and sat on the bride's side of the aisle? Personally, my fingers are crossed that it'll turn out that Mark Hamill just happens to show up to perform the wedding ceremony. Then again, maybe Hamill will visit Sheldon in his dreams to help assuage any pre-wedding jitters. If Bob Newhart's character could appear in a dream and Katee Sackhoff could appear in a fantasy, we shouldn't rule out Hamill turning up in an unexpected way. Force ghost, perhaps?
I'm guessing Teller at least will play himself for the finale, presumably to do tricks of some sort. Kathy Bates and Lauren Lapkus are more curious. They could certainly play characters rather than themselves. Sheldon's family is mostly spoken for between the last 11 years of The Big Bang Theory and now Young Sheldon, but either or both of these actresses could play a member of Amy's family. Maybe Kathy Bates could reprise her role from Disjointed! It was another Chuck Lorre show, and stranger things have happened.