The ongoing 12th season of "The Big Bang Theory" is its last. So you can bet that in their final go-around, the show will try to recruit just about every guest star in the galaxy. But TBBT has already had a nerd's fantasy of astronauts, physicists and Spock. Ahead of its series finale, TheWrap looks at some of the show's most memorable cameos. Excelsior!
"Hot in here? Must be Summer." How many times has "Firefly" star Summer Glau heard that one? In this Season 2 episode, she has to endure the advances of both Howard and Raj as they try to pick her up while traveling on a train.
The show has had a lot of fun with the energetic Christine Baranski playing Leonard’s mom over the years, starting with an appearance in Season 2. Both she and Laurie Metcalf as Sheldon’s mom would cross paths during a Season 8 sweeps week.
In a cameo worthy of the Marvel Cinematic Universe from Season 3, a grumpy Lee wearing a silk Fantastic 4 robe wonders why a giddy Sheldon won't leave him alone.
Judy Greer guest starred as Dr. Elizabeth Plimpton in “Big Bang” Season 3. As has been consistent with many of her characters, she starts off appearing perfectly charming, if slightly socially dysfunctional, but ends up going off the rails as she gets a sex-crazed idea to seduce Howard, Leonard and Raj at once.
One of Howard's fantasies gave us this kinky "Star Trek" and "Battlestar Galactica" crossover, with both George Takei and Katee Sackhoff appearing in Howard's bedroom. Sackhoff had previously appeared in Howard's bathtub in Season 3, but this Season 4 moment would be the start of him getting over bedroom fantasies and thinking about Bernadette, played by Melissa Rauch.
The nerds on "Big Bang" have drooled over a lot of scientists and fanboy favorites, but in Season 5, Sheldon literally faints in the presence of Stephen Hawking, who bluntly confirms for Sheldon that he made a mistake in one of his papers about black holes.
The second man to walk on the moon rattled off three different candy-themed space puns to disappointed trick-or-treaters in his brief cameo during the show's fifth season. "I've been on the moon," Aldrin said. "What have you done?"
LeVar Burton has actually made several cameos on the show, but this one from Season 6 stands out. "It surprisingly only took gas money and the promise of free food to get him here!"
Bob Newhart’s role as Arthur Jeffries, aka Professor Proton, starting in Season 6 was so good, he would not only win his first ever Emmy for his work in 2013, but he also eventually became a series regular, feuding with Bill Nye and the rest of the gang in the process.
James Earl Jones told IGN that amazingly, before this Season 7 "Big Bang" cameo, he and Carrie Fisher had never met, with Jones always doing his scenes as Darth Vader inside a sound booth. The segment features Jones and Sheldon pranking Fisher, but even funnier is their story that when they finally met, Fisher greeted Jones as "Dad!"
"Big Bang" got Adam West to rank all the movie and TV Batmans, putting himself at the top and George Clooney all the way at the bottom, even behind Lego Batman. "I never had to say I'm Batman. I showed up and people knew I was Batman," West joked in Season 9.
In this Season 9 episode, Howard propositioned Elon Musk for a chance to go to Mars when he happened to bump into him washing dishes at a homeless shelter on Thanksgiving. Apparently Musk isn't shy about eating someone's leftover pumpkin pie.
While we had already met Keith Carradine as Penny’s father, this Season 10 episode featuring Jack McBrayer and Katie Sagal as Penny’s brother and mother showed a new side to her family as they worried whether Leonard’s family might look at them as just white trash. McBrayer is especially good at playing a wholesome, country bumpkin drug dealer.
The Microsoft founder’s first appearance came in Season 11, when Leonard staked out Bill Gates’s hotel to see him after getting a tip from Penny, despite her pleading with him to stay at home and not get in the way of her work.
“Big Bang” show runners made a big push to land Mark Hamill, Luke Skywalker himself, to appear in the Season 11 finale and act as the officiant for Sheldon’s wedding, taking over from a snubbed Wil Wheaton. Howard managed to secure Hamill for the wedding after finding his lost dog, Bark Hamill (“It could’ve been Honey Glazed Hamill”).
Kathy Bates and Teller
Ahead of the Season 11 finale, Kathy Bates and the quiet half of magician duo Penn and Teller were cast as Amy’s parents. Bates even replaced Annie O’Donnell, who briefly appeared as Amy’s mom back in Season 9. The couple have since returned in its final season.