Carrie Fisher and James Earl Jones, who played Princess Leia and Darth Vader in Star Wars respectively, had never met in real life before this episode, even though they play major characters in the original Star Wars movies. James Earl Jones would always be in a sound booth providing the voice of Darth Vader, and Carrie Fisher would be on set with David Prowse, who provided the physical acting of Darth Vader. This is paralleled in their scene together in this episode where we see Carrie Fisher on-screen , but only hear the voice of James Earl Jones, who is off-screen.
The names of the possible guests for Sheldon-Con, as seen on his white-board, are as follows: Zachary Quinto, Patrick Stewart, (William) Shatner, Harrison Ford, George Lucas, Mark Hamill, Matt Smith, Billy Dee Williams, Simon Pegg, (Jon) Favreau, Ian McKellen, Stan Lee, Andy Serkis, Martin Freeman, Wil Wheaton, Ahmed Best, Robert Downey Jr., Leonard Nimoy, Bill Nye, Carrie Fisher, Adam West, Anybody who played Uncle Ben, Anybody who shot Uncle Ben.
Sheldon's whiteboard of possible guests includes Mark Hamill, Harrison Ford and Carrie Fisher, but omits James Earl Jones. Simon Larry, the first two Star Wars films produced (Episodes Iv and V) credit Mark Hamill, Harrison Ford and Carrie Fisher, but not James Earl Jones.