60 celebrities you probably forgot guest-starred on 'The Big Bang Theory'

Sonja Flemming/CBSStephen Hawking became a recurring character on ‘The Big Bang Theory’ after becoming online friends with Sheldon.

The Big Bang Theory” has come to an end.

Since 2007, Leonard, Sheldon, Penny, Raj, and Howard have had their fair share of run-ins with celebrities. Howard rubbed shoulders with Buzz Aldrin when he went to space, James Earl Jones pranked Carrie Fisher, and Adam West was invited to Sheldon’s birthday party. Stars from Bob Newhart to the late Stephen Hawking became recurring characters on the CBS comedy.

Neil deGrasse Tyson and Bill Nye kicked off the show’s 12th and final season. Now that the hit show is over, take a look back at the many stars who have appeared on “The Big Bang Theory.”

“The Conners” actress and “The Talk” cohost Sara Gilbert appeared on the show for several seasons as an experimental physicist.

Cliff Lipsonl/CBSGilbert made her first appearance on the show’s third episode. The photo above is of Gilbert on the show’s second season episode, ‘The Codpiece Topology.’

Before Johnny Galecki reprised his role on the “Roseanne” reboot, his old costar Sara Gilbert appeared on “The Big Bang Theory” until season three as Leonard’s ex and colleague, Dr. Leslie Winkle.

Winkle returned for the show’s 200th episode on season nine to attend Sheldon’s birthday party.

She’s not the only “Roseanne” star who has made an appearance. Laurie Metcalf has played Sheldon’s mum.

Michael Yarish/CBSMary Cooper made her first appearance on season one, episode four. She and Sheldon are seen together above for Sheldon’s wedding on the season 11 finale.

Metcalf has appeared on a handful of episodes as Mary Cooper since season one. We expect to see her again to close out the show.

Charlie Sheen played himself on an episode of season two.

CBSSheen appears on the fourth episode of season two.

Sheen appeared on “The Big Bang Theory” while his CBS show, “Two and a Half Men,” was on TV. Raj tells Sheen at a bar that he’s going to be in People magazine.

You can watch a snippet of the scene here.

“The Good Wife” star Christine Baranski has played Leonard’s high-strung mother since season two.

Monty Brinton/Warner Bros.Dr. Beverly Hofstadter’s first appearance was on season two, episode 15. The photo above shows her on the season 10 premiere.

Over the course of the show, Leonard’s neuroscientist and psychiatrist mother, Beverly, becomes close with Sheldon since they both take an overanalytical approach to nearly everything.

Oscar-winner Octavia Spencer doesn’t have an enjoyable run-in with Sheldon at the DMV.

CBSYou can see Octavia Spencer on season two, episode five.

Spencer plays the DMV clerk who Sheldon annoys until she relents and gives him a learner’s permit just so he’ll leave her be.

“Prison Break” actress Jodi Lyn O’Keefe meets the guys in Vegas after Howard suffers a break-up.

Cliff Lipson/CBSO’Keefe appears on season two, episode 21.

The guys take Howard to Vegas and hire Mikayla (O’Keefe) to pretend she’s Jewish and cheer him up. Howard winds up being just fine with that.

“Terminator: The Sarah Connor Chronicles” actress Summer Glau played herself on an episode of season two.

Michael Ansell/Warner BrosThe title of season two, episode 17, ‘The Terminator Decoupling,’ is a nod to Glau’s role.

Glau shares a train with the group as they head to a conference in San Francisco and everyone but Sheldon tries hitting on her.

Comedian Lewis Black appeared on season three as the university’s entomologist.

Sonja Flemming/CBSHe appeared on season three, episode two.

He reveals his school nickname was “Creepy Crawley” since he loved studying insects since a young age.

“The Wonder Years” actress Danica McKellar goes on a date with Raj.

Sonja Flemming/CBSMcKellar appears on season three, episode 12.

McKellar plays a character from “Babylon 5,” Abby, which just so happens to be Sheldon’s least favourite show.

“Happy Endings” actress Courtney Henggeler plays Sheldon’s twin sister, Missy.

Sonja Flemming/CBSHenggeler reprises her season-one role on season 11.

Missy is the exact opposite of her brainy brother, Sheldon, but she’s proud of her sibling. She’s a main character on the spinoff, “Young Sheldon.”

“Battlestar Galactica” actress Katee Sackhoff appeared as Howard’s fantasy apparition.

Cliff Lipson/CBSKatee Sackhoff appeared on episodes of season three and four.

Howard imagines Katee Sackoff when he’s unsure about his relationship with Bernadette.

“Star Trek” actor George Takei also appeared alongside Sackhoff on season four.

Cliff Lipson/CBSTakei makes an appearance on season four, episode four.

Takei appears to Howard in a fantasy to offer him relationship advice about Bernadette alongside Katee Sackhoff.

Comics king Stan Lee visited the comic-book store the guys frequent.

Cliff Lipson/CBSStan Lee appeared on season three, episode 16.

Sheldon misses seeing Lee in person at the store and winds up getting a restraining order from him after he went to meet him at his house and entered uninvited.

“Ant-Man” actress Judy Greer interviews for a job with Sheldon that quickly turns into much more.

Monty Brinton/CBSJudy Greer can be seen on season three, episode 21.

Greer plays Dr. Elizabeth Plimpton, who winds up having sex with Leonard and Raj after interviewing for a job with Sheldon.

Before he was fighting zombies, Stephen Yeun was fighting with Sheldon on “The Big Bang Theory.”

CBSYeun appears on season three, episode 22.

Yeun played Sheldon’s ex-roommate, Sebastian, who tries to warn Leonard about moving in with him.

Los Angeles Lakers player Rick Fox was Bernadette’s ex-boyfriend, Glenn.

Cliff Lipson/CBSRick Fox shows up on season four, episode 13.

Bernadette dated Glenn, her college professor, for a year.

Sheldon spots Apple’s Steve Wozniak and his wife at a restaurant on season four.

Robert Voets/CBSWozniak appears on season four, episode two.

Sheldon speaks to Wozniak via a “Mobile Virtual Presence Device” he builds of himself, which is essentially a monitor of him on wheels.

“Buffy the Vampire Slayer” actor Eliza Dushku played an FBI agent.

Monty Brinton/CBSEliza Dushku appears on season four’s seventh episode.

Agent Angela Page (Dushku) comes to interview the group when Howard is trying to get clearance for government security at work.

Neil deGrasse Tyson also started in a recurring bit on the show starting on season four in that same episode.

CBSNeil deGrasse Tyson first appears on season four, episode seven.

The astrophysicist hit it off with Raj, but was immediately dismissed by Sheldon, who holds him responsible for Pluto’s demotion as a planet. He’ll be back on the 12th season premiere when he gets into a Twitter fight with Raj.

“Reading Rainbow’s” LeVar Burton has appeared on the show multiple times.

Sonja Flemming/CBSBurton has been on the show during seasons four, six, and eight.

Burton appeared on an episode of Sheldon’s online show “Fun With Flags” to discuss “Star Trek” flags, since the actor appeared on “The Next Generation.”

Keith Carradine popped up as Penny’s father, Wyatt.

Monty Brinton/Warner Bros.Wyatt made his first appearance on season four of ‘The Big Bang Theory.’

Wyatt comes to visit his daughter on season four’s ninth episode and is thrilled about Penny dating someone with a college degree. The only problem is that they’re not together anymore. Wyatt just doesn’t know that.

Wyatt returns for the final season of “The Big Bang Theory” to tell his daughter he supports her whether or not she wants a child.

“Arrested Development” star Jessica Walter was a leading donor to the university where Leonard and the guys work.

CBSWalter played Mrs. Latham on season four, episode 15.

Mrs. Latham (Walter) took a liking to Leonard and he decided to sleep with her in order for the university to get the funding they needed.

“Silicon Valley” actor Josh Brener played Stuart’s friend and coworker, Dale.

CBSBrenner made his first appearance as Dale on season five, episode 10.

You probably recognise him as Big Head from the HBO series. Brenner appeared on two episodes of the show during seasons five and six.

“Star Trek” actor Leonard Nimoy didn’t appear in person, but he did voice a toy figurine of his character.

Monty Brinton/CBSYou can hear Nimoy voice the toy Spock who haunts Sheldon on season five, episode 20.

Nimoy voiced Sheldon’s conscience in the form of a Spock toy he referred to as “Little Spock.”

Regina King has appeared as the Human Resources administrator who has had to set Sheldon straight in the past.

Michael Yarish/Warner Bros.King joined the show as Janine Davis on season six, episode 12.

Because Sheldon takes everything so literally, Janine Davis (King) has had to inform the scientist in political correctness after a sexual harassment complaint was filed against him.

Davis makes an appearance on the 12th season when Amy loses it at her own reception in front of several Nobel Prize winners.

Bob Newhart started a recurring role as Sheldon’s beloved childhood TV star, Professor Proton.

Monty Brinton/CBSNewhart’s first appearance is on season six, episode 22.

Arthur Jeffries/Professor Proton was hired by Sheldon and Leonard to entertain the two of them. Eventually, he dies on the show, but returns as a spirit (think a “Star Wars” Force ghost) to give Sheldon advice over the years.

Newhart appeared on the show’s finale season on season 12, episode five.

Buzz Aldrin appeared as himself in a YouTube video handing out candy to kids.

Monty Brinton/CBSAldrin appeared on season six, episode five.

After Howard starts boasting to all of his friends about going to space, he gets sent a video of Aldrin handing out candy on Halloween, telling each and every single one that he went to space.

“America’s Got Talent” judge Howie Mandel steals a moment of glory from Howard.

CBSMandel appears on season six, episode four.

Howard returns from space and when he hears people cheering “Howie” at the airport he mistakes the cheers to be for him. Instead, reporters are waiting for Howie Mandel.

Stephen Hawking had a recurring role on the show until he died in March.

Sonja Flemming/CBSHawking first appears by voice only on season six, episode six.

Sheldon’s relationship with Hawking began when the two start playing “Words With Friends” online.

Hawking later attended Sheldon’s birthday party via Skype and sang to him and encouraged him to marry Amy. The show paid tribute to Hawking by sending Amy and Sheldon a wedding present from him.

Bill Nye becomes friends with Sheldon on the show’s seventh season.

Monty Brinton/CBSBill Nye started appearing on the show on season seven’s seventh episode.

On his first appearance, Nye tells Professor Proton (Bob Newhart) that his science show was inspired by his own. Penny refers to Nye as the “creepy old guy from ‘Dancing With the Stars.'”

Nye appeared on the 17th season of the reality show.

Nickelodeon star Josh Peck appeared as a comic shop rival of Stuart’s.

Monty Brinton/CBSJosh Peck can be seen on season seven, episode 13.

Bernadette and Stuart drop by Jesse’s popular comic store. Though they have a Batman comic she’s looking for, Bernadette doesn’t like the way Stuart is treated by Jesse and the two leave.

Sheldon meets and becomes quick friends with James Earl Jones and the two prank Carrie Fisher.

Robert Voets/CBSJames Earl Jones and Fisher make an appearance on season seven, episode 14.

Sheldon finds the Darth Vader actor eating at a restaurant and the two get along so well that they wind up going to a carnival together and singing a “Lion King”-themed karaoke. During their adventures that evening, they stop at Fisher’s house, ring her doorbell, and then run off. Fisher is not amused and says she knows it was Jones.

They weren’t the only “Star Wars” actors to make an appearance on the show. Mark Hamill had a surprise cameo on the show’s 11th season.

Michael Yarish/CBSYou can see Mark Hamill on season 11, episode 24.

Hamill popped up to officiate Sheldon and Amy’s wedding as himself.

According to The Hollywood Reporter, Hamill accepted an invite to be on the show without seeing a script.

Billy Bob Thornton played urologist Dr. Oliver Lorvis.

Michael Ansell/WBEIBilly Bob Thornton appears on season eight, episode seven.

Lorvis heads to Penny’s apartment to give her roses after mistaking a cue during a sales call for something more. Sheldon originally mistakes him for a deliveryman.

Penny thinks Lorvis is a bit creepy, but the guys wind up hanging out with him after discovering he has a really cool, geeky basement filled with classic posters and video games.

Raj spots “Firefly” star Nathan Fillion eating lunch at a restaurant.

Michael Yarish/Warner Bros. EntertainmentNathan Fillion appears on season eight, episode 15.

Fillion first denies that he’s an actor, but then finally gives in. Fillion gets frustrated as Raj then questions whether or not Fillion actually is the “Firefly” star.

“Malcolm in the Middle” mum Jane Kaczmarek plays a psychiatrist who Leonard visits.

Michael Yarish/Warner Bros. Entertainment Inc.Jane Kaczmarek appears on season nine, episode 12.

Leonard plans to pretend to be a patient, but Dr. Gallo (Kaczmarek) winds up getting both Leonard and Penny to open up about their relationship.

Howard meets Tesla founder Elon Musk while serving dinner to the homeless.

Monty Brinton/CBSElon Musk appears on the ninth episode of season nine.

The two share a piece of pumpkin pie as Musk tells Howard he’s always looking for engineers.

June Squibb appears as Sheldon’s grandma (Meemaw) on season nine.

Michael Yarish/CBSJune Squibb appears on season nine, episode 14.

Sheldon’s Meemaw finally visits in the ninth season and has a few opinions about Sheldon’s girlfriend (and soon-to-be fiancé) Amy.

Adam West heads to Sheldon’s birthday party.

Monty Brinton/CBSAdam West appears on season nine, episode 17.

Raj, Howard, and Leonard discuss the best Batman actors with the TV Dark Knight on the drive over to Sheldon’s surprise party.

Judd Hirsch appears as Leonard’s father for the season nine finale.

Monty Brinton/Warner Bros.Hirsch is on season nine, episode 24.

We quickly learn Alfred Hofstadter (Hirsch) does not get along with his ex-wife, Beverly (Christine Baranski). Alfred winds up taking a liking to Sheldon’s mum, Mary.

Katey Sagal appears as Penny’s mum, Susan, on the season 10 premiere.

Monty Brinton/Warner Bros.Katey Sagal is seen on season 10, episode one.

This cameo is extra special if you know that Sagal previously played Kaley Cuoco’s mother on ABC’s “8 Simple Rules.”

“30 Rock” fans may have noticed Jack McBrayer played Penny’s brother, Randall.

Monty Brinton/Warner Bros.Randall also appears on the season 10 premiere. He’s to the far left in the photo.

In the past, Penny said he went to jail for making homemade meth.

Sheldon goes to a taping of “The Ellen DeGeneres Show” with a co-worker.

CBSEllen can be seen on season 10, episode nine.

Sheldon has no idea who DeGeneres is, but he enjoys his time at the show.

“Do people know about her?” Sheldon asks his friend Bert at a taping of the daytime talk show. “She’s delightful.”

Pamela Adlon lends her voice to Howard and Bernadette’s baby throughout season 10.

Amanda Edwards/Getty Images, Monty Brinton/CBSPamela Adlon voices the baby starting on season 10, episode 11.

If you thought Halley’s voice sounded familiar, it belongs to the “Better Things” actress and comedian.

Christopher Lloyd plays an older man named Theodore, who moves into Sheldon’s room.

CBSLloyd appears on season 10, episode 10.

Theodore moves into Sheldon’s old bedroom briefly and Penny and Leonard are baffled to find him sitting in Sheldon’s favourite spot in the living room.

Bill Gates visits Penny at work during season 11.

Erik Voake/CBSBill Gates appears on season 11, episode 18.

Sheldon doesn’t believe Penny is really meeting with Gates since he visits on April Fool’s Day.

Jerry O’Connell appears as Sheldon’s brother, Georgie Cooper Jr.

Michael Yarish/Warner Bros. Entertainment Inc.Jerry O’Connell appears on season 11, episode 23.

Georgie is Sheldon’s older brother who bullied him when they were younger. Sheldon’s mum says she won’t come to his wedding unless Georgie is invited.

George Cooper Jr. reappeared on season 12, episode four when Leonard Skyped him to ask about one of Sheldon’s childhood friends.

Dean Norris plays US Air Force officer and engineer Colonel Richard Williams.

Monty Brinton/Warner Bros.Dean Norris appears on five episodes of season 10 and one episode of season 11.

On season 10, he tries to get in touch with Raj and Howard about their navigation system.

Kathy Bates appears as Amy’s mother at her wedding to Sheldon.

Michael Yarish/CBSKathy Bates appears on season 11, episode 24.

Bates appeared again on the season 12 premiere and later on the season’s eighth episode where Sheldon spends time with her.

Teller appears as Amy Farrah Fowler’s father on the season 11 finale.

Michael Yarish/CBSTeller, of Penn and Teller, appears on season 11, episode 24.

The usually silent magician surprised fans by speaking two words on the episode: “Thank you.”

“We contacted him and he was super-excited about doing it,” “Big Bang Theory” executive producer Steve Holland told Entertainment Weekly. “He was actually bouncing back and forth. He was directing a play in Chicago and doing his Penn and Teller show in Vegas, but he was like, ‘Don’t worry. We’ll work out the logistics. I really want to be there to do this.'”

Teller appeared again on episode eight of the final season where he spoke even more and took some time to bond with Sheldon.

Sean Astin plays a physicist who proves a theory Sheldon and Amy have been working on.

Michael Yarish/CBSAstin plays Dr. Greg Pemberton on the show’s final season. He first appears on season 12, episode 13.

Dr. Greg Pemberton (Astin) is one of two physicists in Chicago who accidentally confirms the Super-Asymmetry paper Sheldon and Amy publish. He appears a few times on the final season.

Kal Penn plays Dr. Campbell, the other physicist who initially confirms Sheldon and Amy’s science paper.

Michael Yarish/Warner Bros. EntertainmentPenn’s first appearance on ‘The Big Bang Theory’ is also season 12, episode 13.

On his show’s second appearance he tries to take credit for Sheldon and Amy’s scientific paper.

Comic-book store owner Kevin Smith finally appears on the show’s final season.

Michael Yarish/CBSKevin Smith made his first show appearance on season eight briefly. We finally see him on season 12, episode 16 with a few other stars.

Smith is part of a secret celebrity “Dungeons & Dragons” game Wil Wheaton hosts in his home.

Previously, Smith’s voice was heard on season eight, episode 20 of the show. Smith calls into a podcast taping about Penny’s ape movie with Wheaton. It turns out Smith is one of the few people who enjoyed the movie and he invites Penny to audition for a role in “Clerks 3.”

“True Blood” star Joe Manganiello is also part of Wil Wheaton’s secret celebrity “Dungeons & Dragon” club on the show.

Michael Yarish/CBSManganiello appears on season 12, episode 16.

Manganiello didn’t have to act. He really is a big fan of “D&D.” The actor told Stephen Colbert he hosts his own games in his basement with celebrities like “Saturday Night Live’s” Taran Killam.

He has even stopped by the UPMC Children’s Hospital of Pittsburgh with his brother to host a session of the game.

Basketball player Kareem Abdul-Jabbar appeared as himself during a game of “Dungeons & Dragons.”

Michael Yarish/CBSAbdul-Jabbar also appears on season 12, episode 16.

Nobel prize winner professor George Smoot appears as himself on season 12.

Michael Yarish/CBSSmoot appears on season 12, episode 18.

Smoot received the Nobel Prize in physics in 2016. Smoot is one of several Nobel Prize winners to receive a package from Sheldon. He tosses it in the garbage without opening it.

Professor Kip Thorne appears as himself and also receives a package from Sheldon.

Michael Yarish/CBSThorne appears on season 12, episode 18 right after George Smoot.

Thorne received the Nobel Prize in physics in 2017 and turns down a package from Sheldon.

Professor Frances H. Arnold is the last Nobel Prize winner to receive a package from Sheldon.

Michael Yarish/CBSArnold also appears on season 12, episode 18.

Arnold won the Nobel Prize for chemistry in 2018. She later meets Sheldon and Amy at their reception.

Sarah Michelle Gellar played herself on the series finale.

CBSThis wasn’t the cameo we were expecting.

Raj sits next to her on the plane ride to Amy and Sheldon’s award ceremony and winds up convincing her to tag along as his guest.

“I have been a huge ‘Buffy’ fan for years. I’ve re-watched that show probably more than any other. And a lot of the writers are big ‘Buffy’ fans, too,” showrunner Steve Holland told The Hollywood Reporter. “[Creator] Chuck [Lorre] spoke to her on the phone and at the beginning [of the call], she said her family loves ‘Big Bang Theory.’ Then it was just a matter of working out scheduling.”

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