Over the course of The Big Bang Theory's 12-season run, plenty of famous faces have ventured to Pasadena, Caltech, the Cheesecake Factory and the friends' various apartments to provide guidance, laughs and more for our favorite group of knowledgeable nerds.
From Star Wars stars to comic legends to Sheldon's ongoing feud with Wil Wheaton (plus Sheldon's ongoing feud with Brent Spiner and Sheldon's ongoing feud with Joel Schumacher...) there's been no shortage of celeb cameos on the beloved CBS sitcom, with most stars playing hilariously exaggerated versions of themselves.
Here's a look at just some of the Big Bang cameos we've nerded out over in the last 12 years:
The TV legend is one of Big Bang's most beloved guest stars, first appearing in season six as Dr. Arthur Jeffries, aka Professor Proton, a former children's TV host whom Leonard and Sheldon (especially Sheldon) idolized as kids. Professor Proton becomes a father figure to Sheldon, and despite the character's death in season seven, returns for several more appearances as as a "force ghost" -- even donning classic Jedi robes -- to offer advice when his protege is struggling. Even more endearing? The role won Newhart his first-ever Emmy!
The theoretical physicist made several appearances on The Big Bang Theory throughout the years, first receiving a shout out as the man Sheldon believed to be "perhaps my only intellectual equal." Hawking later guested on the show as a visiting lecturer, and made several voice and video cameos -- even appearing at Sheldon's birthday party via Skype in the show's 200th episode, "The Celebration Experimentation."
The show also paid tribute to Hawking, who died in March 2018, in a deleted scene from the season 11 finale. After Sheldon and Amy tied the knot, they received a gift from the famed scientist, a pocket watch engraved with the message that it was "about time" for them to get hitched.
The Marvel Comics mastermind is known for his cameo appearances in every MCU movie, but he also starred as himself in season 3, episode 16 of The Big Bang Theory, entitled "The Excelsior Acquisition." After Sheldon misses out on his chance to meet Lee at the comic book store, Penny finds out his address and the two travel to his house to shoot their shot -- and end up with a restraining order for their troubles!
Mark Hamill, Carrie Fisher and James Earl Jones
It wouldn't be Big Bang without a few key Star Wars references, and over the years, the show has featured cameos from some of the franchise's biggest names. Mark Hamill married Amy and Sheldon in the season 11 finale, "The Bow Tie Asymmetry," while Sheldon and James Earl Jones teamed up to ding-dong ditch Carrie Fisher in the season 7 episode "The Convention Conundrum."
William Shatner and Leonard Nimoy
On the Star Trek side of things, Big Bang scored some of the franchise's most famous faces (and voices) in Shatner and Nimoy, though it took some time. After years of references to Capt. James T. Kirk, Shatner finally appeared as himself in a celebrity Dungeons & Dragons game in season 12's "The D&D Vortex."
While Nimoy never appeared in person on the sitcom prior to his 2015 death, he did provide the voice for Sheldon's Spock figurine in the season five episode "The Transporter Malfunction." The actor's son, Adam Nimoy, also interviews Sheldon for a documentary on his father in the season nine episode "The Spock Resonance." And, of course, there was the infamous napkin.
George Takei and Katee Sackhoff
These two sci-fi fan favorites teamed up for a silly but revealing cameo in the season four episode "The Hot Troll Deviation." Sackhoff reprised her season three role as Howard's fantasy dream girl, but this time, the Battlestar Galactica star was joined by Takei, who raised questions about Howard's sexuality before he was able to realize the fact that his true feelings were for Bernadette -- which ultimately led the two to reconcile.
The Star Trek star has been a recurring cameo favorite on Big Bang Theory since the early seasons, starting out as Sheldon's nemesis -- "WHEATONNN!!!" -- before becoming friendly with the gang in later years, helping Penny out with her acting career, introducing some of his famous friends and stepping up to perform Sheldon and Amy's wedding when Mark Hamill got too emotional.
Yet another Star Trek actor to grace the Big Bang sound stage, Burton has made several cameos on the sitcom -- including two contractually obligated appearances on Sheldon's web series, "Fun With Flags!"
Another legend of comics canon, West fulfilled Sheldon's lifelong dream of having Batman attend his birthday in the show's 200th episode, "The Celebration Experimentation." Even better: He held his own in the guys' "Best Batman" debate!
The second man to walk on the moon has made several cameos as himself in film and television, but on Big Bang, his role comes as a cautionary tale. After Howard becomes a little too fixated on his own career accomplishments, Raj sends him a viral video of Aldrin passing out Mars bars, Milky Ways and Moon Pies to children on Halloween -- along with some unsolicited boasting. "I walked on the moon," he brags to one trick-or-treater. "What have you ever done?"
The whole gang gets excited to meet the Microsoft guru when he comes to visit Penny at work in a season 11 episode titled "The Gates Excitation" -- but only one of them has a history with one of their tech heroes. Leonard tells Raj and Howard that he met Gates as a kid and cried all over him, and it happens once again when they run into him in his hotel lobby. "Oh, now I remember!" Gates exclaims as Leonard starts to blubber. "Would you like a tissue?"
The Science Guy himself has made two appearances on Big Bang as a rival of Professor Proton, a not-so-helpful friend of Dr. Neil deGrasse Tyson -- and yet another celeb who takes out a restraining order against Sheldon.
The Back to the Future star channeled Doc Brown's best crazy smarts in the season 10 episode "The Property Division Collision," where he played Theodore, a homeless man Sheldon rents his room to in order to get back at Leonard -- who actually ends up helping to solve the conflict between the two.
Nathan Fillion and Summer Glau
The Firefly stars both snapped reluctant selfies with the guys during their cameo appearances as themselves on Big Bang, with Fillion appearing in season eight's "The Comic Book Store Regeneration," and Glau starring in season two's "The Terminator Decoupling."
Another former Joss Whedon series star, Dushku played FBI Special Agent Angela Page, who was tasked with interviewing Howard's friends in order to grant him top-level security clearance in the season four episode "The Apology Insufficiency."
Kevin Smith and Joe Manganiello
Wil Wheaton's celebrity Dungeons & Dragons game in season 12's "The D&D Vortex" didn't just attract William Shatner. Noted celebrity nerds Kevin Smith and Joe Manganiello also showed up to play!
While not quite as nerd-tastic as the rest of the show's most memorable cameos, The Big Bang Theory has recruited an impressive list of talent to play the mothers of the main characters throughout the years. Laurie Metcalf was first, turning up in season one as Sheldon's mother, Mary Cooper. (Metcalf's real-life daughter, Zoe Perry, plays a younger version of the character on the Big Bang prequel series, Young Sheldon.)
The Good Fight star Christine Baranski first appeared as Leonard's mother, Dr. Beverly Hofstadter, in the season two episode "The Maternal Capacitance," while Katey Sagal reunited with her Eight Simple Rules onscreen daughter, Kaley Cuoco, to play Penny's mom, Susan. And Kathy Bates played Amy's mother, Mrs. Fowler, in the season 11 finale that featured Amy and Sheldon's wedding, after the role was previously played by Annie O'Donnell in a video chat in previous seasons.
And of course, we can't forget Meemaw! Oscar nominee June Squibb made her first appearance as Sheldon's favorite family member in the season nine episode "The Meemaw Materialization," while Annie Potts plays the character on Young Sheldon.
The Big Bang Theory's hour-long finale airs Thursday, May 16 at 8 p.m. ET/PT on CBS.