Entering the 2018 fall season, fans were greeted with the news that Season 12 of The Big Bang Theory will be its last. TBBT has been an anchor of the CBS lineup and a solid performer in the ratings since its debut episode in 2007. It would seem there is still plenty of life left in the show, but like other successful hits -- such as Mary Tyler Moore, Seinfeld, The Cosby Show, Cheers -- it's leaving before it runs out of gas (like Laverne & Shirley) and before people get sick of having it around.
The Big Bang Theory focuses on Sheldon Cooper, Leonard Hofstadter, Rajeesh "Raj" Koothrappali and Howard Wolowitz, scientists at the California Institute of Technology; the women in their lives, Penny (whose last name has never been revealed), Bernadette Rostenkowski and Amy Farrah Fowler; as well as various friends, frenemies and others. TBBT has opened a window on geek culture to a national audience. Along the way, it featured many guest appearances from some of the most well-known and beloved icons in physics, computing, SF and fantasy -- Battlestar Galactica, Star Trek and Star Wars -- and, of course, comics. Here, CBR ranks the best cameos over the past 11 seasons. For our purposes, we're not looking at recurring characters who are part of the fabric of the show. Our focus is on the ones who've popped up only a few times, or even just once.
33 BOB NEWHART
Comedy legend Bob Newhart first appeared in Season 6's "The Proton Resurgence" as Arthur Jeffries, host of the kids' science show Professor Proton. Sheldon and Leonard hire him to do a personal appearance, and find that Jeffries is rather glum. Typecast, Jeffries couldn't find other work in television or as a scientist, and supports himself doing kids' parties.
Doing it for two grown men skeeved him out, but Sheldon and Leonard let him know how much he inspired them and others, and their successes are his successes. Newhart won the 2013 Emmy Award for Outstanding Guest Actor in a Comedy Series -- amazingly, the first Emmy in his career. He reprised the role four times on TBBT and twice on the spinoff Young Sheldon.
32 LEONARD NIMOY
It's no surprise that Sheldon would revere Spock from Star Trek as well as Leonard Nimoy, the first Spock in TV and film. In Season 2's "The Bath Item Gift Hypothesis," Penny's Christmas gift to Sheldon is a Cheesecake Factory napkin autographed by Nimoy, which thrills him because Nimoy wiped his mouth with it. Sheldon entertains the thought of using it to clone Nimoy.
In Season 5's "The Transporter Malfunction," Penny gives Sheldon and Leonard vintage collectible Star Trek transporter play sets. Sheldon breaks his and switches it with Leonard's. But Sheldon's Spock action figure -- voiced by Nimoy -- first warned Sheldon not to open the set and then guilts him into admitting his wrongdoing.
31 STAN LEE
Stuart's comic shop gets a big guest for a personal appearance -- Stan Lee, in Season 3's "The Excelsior Acquisition." Unfortunately, it's the same day Sheldon has to go to traffic court for running a red light when he took Penny to the hospital in "The Adhesive Duck Deficiency." Of course, Sheldon couldn't just pay the fine; he represents himself in court, insults the judge, and gets thrown in the clink.
After he gets out -- apologizing to the judge was less distasteful than using a metal jail toilet -- Penny finagles Stan Lee's address and takes Sheldon there. In the end, Sheldon is happy to get Stan Lee's autograph ... on a restraining order, matching the one he has from Leonard Nimoy.
30 STEPHEN HAWKING
The late theoretical physicist and cosmologist Stephen Hawking is a legend to Sheldon, Leonard, Howard and Raj. In the series pilot, Howard does a quick impression of Hawking's computer modulated voice. Hawking himself first appears in Season 5's "The Hawking Excitation," in which CalTech has Howard maintain Hawking's wheelchair. Sheldon tries to kiss up to Howard so he can meet Hawking but, being Sheldon, ruins his chance by dropping a lot of casual insults.
Hawking appeared on the show seven times, and is remembered in a deleted scene in the Season 11 finale. He gives Sheldon and Amy a wedding gift: a pocket watch inscribed "Sheldon, I'm so glad you finally married Amy. It's about time. Ha ha ha, love, Stephen."
29 KEITH CARRADINE
Character actor Keith Carradine made three appearances on The Big Bang Theory as Penny's father, Wyatt. Carradine's first appearance was in Season 4's "The Boyfriend Complexity" when Wyatt comes to Pasadena to visit Penny. Unfortunately for her, Wyatt's visit happens shortly after she and Leonard have broken up. To Leonard's delight, Penny wants to pretend they're still a couple for Wyatt.
Penny can't keep up the ruse and admits the truth to Wyatt, who is insulted that she lied to him. But he privately begs Leonard to stay with her because he's far better than any of Penny's past dim-bulb loser boyfriends: "I can't go back to the skateboard idiots, the white rappers and all those sweaty dumb [guys] with their backwards hats."
28 KATEY SAGAL
Penny had mentioned her mother Susan in several episodes before we saw her on screen. Take, for example, Season 7's "The Status Quo Combustion," in which Penny calls Susan to let her know she's engaged to Leonard but not pregnant. Leonard and Penny get married in Las Vegas in the Season 9 premiere "The Matrimonial Momentum."
In "The Conjugal Conjecture," the Season 10 premiere, we meet Susan, played by Katey Sagal. She, Wyatt and Penny's brother Randall, played by Jack McBrayer, come to Pasadena for Penny's and Leonard's renewal of vows. Sagal's presence was a reunion for her and Kaley Cuoco; they previously played mother Cate and daughter Bridget on 8 Simple Rules for Dating My Teenage Daughter from 2002 to 2005.
27 KATEE SACKHOFF
Katee Sackhoff starred on the Sci Fi Channel's revival of Battlestar Galactica from 2004-2009 as Lt. Kara "Starbuck" Thrace. In the original 1978 series on ABC, Starbuck was played by a male actor, Dirk Benedict. This reimagined version of Starbuck was a fantasy figure for Howard, who imagined himself sharing a bubble bath with her in the Season 3 episode "The Vengeance Formulaton."
Fantasy Katee reminds him there's a real woman, Bernadette, who loves him. Howard is more interested in Fantasy Katee, but the dream is shattered by a bellow from Howard's off-screen mother, Mrs. Wolowitz. Still, Howard is inspired to propose to Bernadette, but she turns him down. Fantasy Katee appears in Season 4's "The Hot Troll Deviation" in another of Howard's dreams.
26 MARK HAMILL
As the face (and body) of Luke Skywalker in the Star Wars franchise, as well as the voice of The Joker in the Batman: The Animated Series show -- not to mention his turns as The Trickster on the 1990 and 2014 live-action TV versions of The Flash -- Mark Hamill has more than enough geek cred to spare.
He appears in "The Bow Tie Assymmetry," the Season 11 finale. Through the kind of contrivance that can only happen in TV sitcoms -- Howard finds his lost dog, and Hamill grants him any favor he wants -- Hamill officiates at Sheldon and Amy's wedding. Before he can, he has to stall by fielding questions about Star Wars from the wedding guests.
25 JAMES EARL JONES
Another figure from the Star Wars series, James Earl Jones, the voice of Darth Vader, appears in Season 7's "The Convention Conundrum." Sheldon, Leonard, Raj and Howard try to buy tickets online to the San Diego Comic-Con, but get the 15,211th place in line -- and then get shut out. Leonard, Raj and Howard consider buying tickets from a scalper, but Sheldon resolves to hold his own comics convention, despite having no knowledge of how to do it, no venue and no guests, either high- or low-profile.
Through some Internet sleuthing, Sheldon finds Jones at his favorite sushi restaurant. Improbably, Jones takes a liking to Sheldon and they gad about town. In the end, Jones invites Sheldon and his friends to Comic-Con.
24 CARRIE FISHER
The late Carrie Fisher, Star Wars' Princess Leia, also appears in Season 7's "The Convention Conundrum." James Earl Jones' jaunt around town with Sheldon takes them to a modest home. Sheldon asks, "Whose house is this?" Jones answers, "Carrie Fisher. And she's a little crazy, so get ready to run." Jones rings the bell and runs; Sheldon follows. Fisher, wielding a baseball bat, comes out and shouts, "IT'S NOT FUNNY ANY MORE, JAMES!" Jones replies, "THEN WHY AM I LAUGHING?!"
Happily, filming that episode brought Jones and Fisher together for the first time. Because Jones did his Darth Vader work in a recording studio and not on set, he'd never acted with her.
23 NEIL DEGRASSE TYSON
Neil deGrasse Tyson is an astrophysicist, cosmologist, director of the Hayden Planetarium and host of the 2014 documentary series Cosmos: A Spacetime Odyssey on Fox and the National Geographic Channel. Tyson has a conversation with Raj at CalTech in Season 4's "The Apology Insufficiency." Sheldon butts in and confronts Tyson, complaining that he demoted Pluto from being a planet. Tyson rightfully points out that wasn't his call, but the decision of the International Astronomical Union.
Tyson is also slated to appear in the Season 12 season premiere, "The Conjugal Configuration." Raj, while being interviewed on a news program about a pending meteor shower, winds up starting a Twitter war with Tyson, who calls him out.
22 LEVAR BURTON
Original Star Trek: The Next Generation cast member LeVar Burton showed up three times on The Big Bang Theory. The first was in Season 4's "The Toast Derivation," when Sheldon sends Burton a Twitter invitation to join his social group. But the sight of Sheldon's other friends -- comics store owner Stuart Bloom, Caltech scientist Barry Kripke and Penny's ex-boyfriend Zack -- singing "Walking On Sunshine" karaoke scares Burton away.
Burton returns in Season 6's "The Habitation Configuration" as a guest on Fun With Flags, lured by the promise of money, gas and free lunch. He makes a return visit to Fun With Flags in Season 8's "The Champagne Reflection" because Sheldon pledged to delete his contact information as Burton watched.
21 MIKE MASSIMINO
Of the four guys on The Big Bang Theory, Howard likes to remind Sheldon, Leonard and Raj that what he does has real-world uses. Also, he is the only one who has been to the International Space Station. Helping him get there was astronaut Mike Massimino, who made six appearances -- four in Season 5, two in Season 7 -- as himself.
Massimino first appeared in "The Friendship Contraction," in which he gives Howard his astronaut nickname "Froot Loops." In subsequent episodes, Massimino, Howard and Russian cosmonaut Dmitri go to the ISS on Expedition 31. In Season 7's "The Table Polarization," Massimino is among Howard's friends trying to talk him out of a second trip to space.
20 BILL GATES
Bill Gates, founder of Microsoft Corp. and co-chair of the Bill & Melinda Gates Foundation, appeared in person in Season 11's "The Gates Excitation." Penny gets to show Gates around on a visit to Pasadena because the Gates Foundation is interested in vaccines her pharmaceutical company makes. Leonard, Raj and Howard excitedly want to meet Gates; Sheldon assumes it's an April Fool's Day prank.
In Season 4's "The Toast Derivation," Raj tells the story of Gates punching out Sheldon, for saying to him, "Maybe if you weren't so distracted by sick children in Africa, you could have put a little more thought into Windows Vista."
19 BUZZ ALDRIN
Howard's trip to the International Space Station in Season 5 made him a celebrity in his own mind. In Season 6's "The Holographic Excitation," Howard annoys everyone by constantly talking about his space travels.
At the end of the episode, Raj shows Howard an online video of legendary astronaut Buzz Aldrin -- the second man to walk on the moon -- at his home giving Halloween candy to trick-or-treaters. Aldrin says to them, "Here's a Milky Way. The Milky Way is a galaxy in space. I've been to space. Here's a Mars bar. I'm an astronaut. This one's a Moon Pie. I've walked on the moon. What have you done?"
18 BILL NYE
Professor Proton's real-world counterpart as the host of a kids' TV science show is Bill Nye, host of Bill Nye, The Science Guy and other shows in that vein. So it's only natural that Nye would show up. He appeared in the Season 7 episode "The Proton Displacement." Leonard encounters Professor Proton in the pharmacy and later, Proton asks Leonard's advice on a paper he's writing about nano-vacuum tubes.
Sheldon becomes jealous that Proton didn't ask him for advice, and later brings Nye along to the laboratory where Leonard and Proton are at work. Nye expresses admiration, but Proton is hostile, insinuating Nye stole his concept. Nye also is slated to appear in the Season 12 premiere, "The Conjugal Configuration."
17 ADAM WEST
In Season 9's "The Celebration Experimentation," Amy wishes to celebrate Sheldon's birthday. Sheldon is against birthday celebrations because of bad memories of being snubbed by the friends he invited to childhood parties. When he was 6, his twin sister told him Batman was coming and he waited all day for him.
This gives Leonard the idea to bring in a real Batman, so they get Adam West to appear. On the ride to the apartment, West banters with the guys over who was the best Batman. He notes that, unlike Christian Bale, he never had to say "I'm Batman," and his costume didn't have fake muscles. He also calls Sheldon "Sherman."
16 GEORGE TAKEI
In Season 4's "The Hot Troll Deviation," Howard is reeling from a recent breakup with Bernadette. He prepares for an evening with Fantasy Katee Sackhoff, but Bernadette also shows up in the fantasy. This leads Fantasy Katee to point out Howard's not over the real Bernadette. Then Fantasy George Takei appears, leading Fantasy Katee to question Howard's interests.
Later, Howard and Bernadette go on a date and afterward, start making out in her car. Fantasy Katee and Fantasy George pop up in the back seat, criticizing Howard's technique. Fantasy Katee says Howard should be more aggressive, while Fantasy George advises taking it slow. Howard makes a move Bernadette doesn't like, proving Fantasy George right.
15 SUMMER GLAU
In Season 2's "The Terminator Decoupling," Sheldon, Leonard, Howard and Raj travel to a symposium in San Francisco. At Sheldon's insistence, they go by train, even though flying from Pasadena costs half as much and doesn't take seven hours. But also on the train is actress Summer Glau, of Firefly, Serenity and The Terminator Chronicles.
Leonard, Howard and Raj all try to muster up the courage to talk to Glau. Howard comes up with a cheesy pickup line, "It's hot in here, it must be Summer," but Raj, with a beer in hand, says it first. When Raj learns the beer is non-alcoholic, he clams up. Howard takes his shot, and scares Glau. And when Leonard gets ready to try, she reaches her stop.
14 NEIL GAIMAN
Although comic book store owner Stuart is often broke, his fortunes change in Season 11's "The Comet Polarization," when science fantasy and comics author Neil Gaiman tweets positively: "Next time you're in Pasadena, check out The Comics Center. Great vibe, old school, the owner really knows his stuff." The guys can't remember meeting Gaiman; they dismissed him when he suggested the Uru metal of Thor's hammer is one of the hardest metals in comics.
Gaiman's tweet brings in so much new business, Stuart changes the register receipt for the first time. He also hires an assistant manager, Denise, who knows comics as well as the guys do. Gaiman is at the store again, and recommends 1602 to Sheldon, who disregards it.
13 ELON MUSK
It's Thanksgiving in the Season 9 episode "The Platonic Permutation," and Amy and Sheldon, who have recently broken up, go to the aquarium as friends. Raj, his girlfriend Emily, and Bernadette go to a soup kitchen to serve Thanksgiving dinner to the homeless. Howard tries to get out of it, but goes too.
The four of them get assigned to washing dishes, but when the chance comes to serve meals, Bernadette, Raj and Emily leave Howard. However, to his surprise, he is joined by Elon Musk, CEO of Tesla and founder of Space X. Musk tells Howard he was reassigned from serving meals to washing dishes because he gave out too much gravy.
12 REGINA KING
Two-time Emmy-winning actor (American Crime, 2015 and 2016) and director Regina King has appeared five times on The Big Bang Theory as Janine Davis, Caltech's administrator of human resources. Davis first appeared in Season 6's "The Egg Salad Equivalency," when Sheldon faced a complaint of sexual harassment from his new assistant. In Sheldon's clueless way, he not only makes his own situation worse but tells Davis about things Leonard, Howard and Raj have said and done.
Indeed, all four of the guys are frequent flyers to Davis' office, Howard in particular because of his horndog ways before he met and eventually married Bernadette. Davis appears once more in Season 6, and once in Season 7, Season 8 and Season 11.
11 KATHY BATES AND TELLER
Amy frequently speaks of her mother, and the picture she paints is of a woman who is bossy, fussy, domineering and represses her daughter. Mrs. Fowler, whose first name is unrevealed, first appears in a video chat in Season 4's "The Desperation Emanation," played by Annie O'Donnell.
Mrs. Fowler, this time played by Kathy Bates, is in Season 11's "The Bow Tie Asymmetry," with her husband Larry, attending Amy's wedding to Sheldon. Larry Fowler is played by Teller of the magic duo "Penn & Teller." True to form, he is largely silent, except when an exasperated Penny yells at Mrs. Fowler; Larry Fowler says, "Thank you!" Mr. and Mrs. Fowler are slated to appear in the Season 12 premiere, "The Conjugal Configuration."
10 JUNE SQUIBB
Sheldon often talks about his grandmother, Connie Tucker, whom he affectionately calls "Meemaw." Indeed, his grandmother is about the only relative he has that he genuinely likes, without any reservation or condescension about their intellect, accomplishments or beliefs. So he was really happy when she came to visit him in Season 9's "The Meemaw Materialization," except for one thing -- she didn't like Amy.
June Squibb played Meemaw in that episode. On the spinoff Young Sheldon, Annie Potts plays the role. Meemaw was absent at Sheldon's wedding in "The Bow Tie Assymmetry" -- producers chalked it up to her being too elderly and frail to make the journey.
9 BRENT SPINER
Sheldon regards Wil Wheaton, of Star Trek: The Next Generation, as his mortal enemy. We learn in Season 3's "The Creepy Candy Coasting Corrolary" it's because Wheaton failed to show for a Star Trek convention Sheldon attended. Wheaton has been a recurring presence on The Big Bang Theory, and in Season 5's "The Russian Rocket Reaction," invites the guys to a party at his house.
Among the guests is Brent Spiner, Wheaton's co-star from The Next Generation. Initially, Sheldon huffily refuses to attend, but goes when he learns Spiner will be there. At the party, Wheaton makes amends to Sheldon by giving him a mint-condition, signed Wesley Crusher action figure ... which Spiner opens, making him Sheldon's new mortal enemy.
8 STEVE WOZNIAK
Steve Wozniak was the co-founder of Apple and developer of the Apple I computer. So naturally, Sheldon was excited to meet him in Season 4's "The Cruciferous Vegetable Amplification," when Wozniak went to dinner at The Cheesecake Factory restaurant where Penny worked. Sheldon doesn't meet Wozniak in person because, at the time, he was obsessed with extending his lifespan, so he was using a robot to go around town in his stead.
Striking up a conversation with Wozniak, Sheldon tells him he has a vintage 1977 Apple. Wozniak says, "You know, if you had it here I'd autograph it for you." Back in his apartment, Sheldon grabs the Apple and races to the restaurant -- but trips on the stairs and breaks it.
7 JUDD HIRSCH
Leonard's father, Alfred Hofstadter, is another family member who was frequently mentioned over several seasons before appearing in person. We finally met him in the Season 9 finale, "The Convergence-Convergence," when he comes to Pasadena for Leonard's and Penny's renewal of vows (although Leonard's brother and sister don't show). Soon, Alfred is bickering with Leonard's icy, disdainful mother Beverly, played by Christine Baranski, who has appeared 13 times.
Alfred bonds with Sheldon's mother Mary, played by Laurie Metcalf, as they both don't like Beverly. Alfred and Mary surprise everyone at the rehearsal dinner by leaving together. In the Season 10 premiere, "The Conjugal Conjecture," we learn they just had a conversation, but enjoy each other's company.
6 JERRY O'CONNELL
Sheldon's older brother Georgie is another character who was often mentioned but not seen on screen. In Season 11's "The Sibling Realignment," we meet Georgie, played by Jerry O'Connell. Sheldon's mother Mary refused to come to his wedding because he wouldn't invite Georgie, so Sheldon and Leonard go fix things.
They find that Georgie now calls himself George, and owns a chain of tire stores. Sheldon is hurt that George mistreated him through childhood. But Leonard tells Sheldon to apologize, and George lets him know he supported the family after their father died, protected Sheldon without thanks, and launched his business on his own since the family money went to Sheldon's education. Sheldon apologizes and invites George to the wedding.
5 HOWIE MANDEL
Howard found his return to Earth from his trip to the International Space Station disappointing. In Season 6's "The Re-Entry Minimization," he has a scary re-entry. Worse, when he returns from Houston to Pasadena, he finds only Bernadette is waiting for him at the airport.
There is a crowd at the airport, and someone shouts, "There he is! Howie! Howie!" Howard, pleased, says to a gaggle of photographers, "Whoa, thank you. Great to be back on Earth." However, behind him is America's Got Talent judge Howie Mandel, who was on the same flight. "Uh, I think they're here for me, Ringo," Mandel says. To his driver, Mandel says, "That nutjob was telling everybody on the plane he's an astronaut."
4 ADAM NIMOY
In Season 9's "The Spock Resonance," Sheldon's frenemy Wil Wheaton arranges for him to be interviewed by Adam Nimoy for the documentary For the Love of Spock, about the character's cultural influence. Sheldon happily agrees. However, this is shortly after Sheldon and Amy had broken up, and he is not over her, even as he protests he has "mastered" Spock's way of denying his emotions.
Adam Nimoy gets Sheldon to show off his prized possessions, which include the napkin with Leonard Nimoy's DNA on it ... and the ring Sheldon was going to propose to Amy with. Adam Nimoy incorporated parts of this episode and interviews with TBBT people into the finished documentary.
3 CHARLIE SHEEN
In Season 2's "The Griffin Equivalency," Raj tells the gang he will be featured in an upcoming issue of People magazine. He is tabbed as one of "30 Visionaries Under 30 Years to Watch," for discovering a minor planet beyond Neptune's orbit. Raj milks the attention for all he can get, including inviting Penny to a reception the magazine is having for the article and telling his parents Penny is his girlfriend.
At one point, he's at the Cheesecake Factory and calls to a man at the bar, "Hey. buddy, I'm going to be in People magazine." The man takes off his sunglasses and turns around; it's Charlie Sheen. "Call me when you're on the cover," he says.
2 BILLY BOB THORNTON
Penny's new job as a pharmaceutical company sales rep is going well, but one day she gets a challenging client: one Dr. Oliver Lorvis, played by Billy Bob Thornton. In Season 8's "The Misinterpretation Agitation," Lorvis comes to Penny's apartment with flowers after she flirted with him on a sales call, thinking he has a shot at romance. This, of course, upsets Leonard, but Sheldon invites Lorvis in.
The guys learn Lorvis is a urologist with many celebrities on his patient roster. They accept his invitation to see his large collection of movie memorabilia. He locks them in and tries to go after Penny again, but gets smitten with Amy. Penny has Lorvis free the guys and lets him know how creepy he's being.
1 CHRISTOPHER LLOYD
In Season 10's "The Property Division Collison," Amy and Sheldon and Penny and Leonard are sorting out new living arrangements. Leonard has moved into Apartment 4A with Penny since they got married, but they've mutually agreed that Amy and Sheldon will stay there; Leonard and Penny will take the bigger Apartment 4B.
In deciding who keeps what from each place, somehow Sheldon finds a reason to keep everything he wants, and Leonard just gives in. Is this enough for Sheldon? Of course not. In a fit of pique, he rents out his bedroom to a homeless drifter, Theodore, played by Christopher Lloyd of Back to the Future fame and Emmy winner for Taxi.