Any show that’s been on TV as long as The Big Bang Theory is sure to rack up an impressive list of guest stars. With everyone from Stephen Hawking to Wil Wheaton to Christine Baranski taking some time to join everyone’s favorite gang of nerds in their many adventures, The Big Bang Theory has possibly had more stars on it than any other sitcom on air.

However, with all of these memorable guest stars, there are still plenty of awesome people who you may have forgotten appeared on TBBT during its nine year run. To help you refresh your memory, here are 12 Famous Guest Stars You Forgot Appeared On The Big Bang Theory.

12. Steven Yeun, The Staircase Implementation (Season 3, Episode 22)

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That’s right, before starring on The Walking Dead as Glenn, Steven Yeun had a very brief appearance on The Big Bang Theory as Sheldon’s roommate before Leonard (named Sebastian, according to IMDb, although he’s not on the show long enough to have his name said).

Yeun appears in a flashback while Leonard is telling Penny about how Sheldon was worse before he moved in with him. Sebastian, moving out of the apartment using the still-working elevator, warns Leonard to “run away, dude.” Leonard says that the cautionary “run fast, run far” should have been his first clue not to move in. Looks like he ignored Sebastian’s advice.

11. George Takei, The Hot Troll Deviation (Season 4, Episode 4)

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The Star Trek actor appeared as himself in one of Howard’s fantasy sequences, along with Battlestar Galactica’s Katee Sackhoff. Takei talked about how it’s “difficult” to be typecast as a science fiction icon. “You try and stretch as an actor, do Strindberg, O’Neill, but all they want is ‘Course laid in, Captain,’” he said.

He appeared again later in the episode, encouraging Howard to court Bernadette and take it slowly. When Sackhoff questions how Takei is qualified to give advice about women, he replies with “I read.” Although Sackhoff disagrees with him and says the two should move more quickly, Takei ends up being right, with Bernadette rebuking Howard and telling him to wait for their relationship to “get there.”

10. Jessica Walter, The Benefactor Factor (Season 4, Episode 15)

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Walter appeared as the very Lucille Bluthe-esque “Mrs. Latham” in one 2011 episode. Mrs. Latham, a rich donor to Cal Tech, demands that Leonard “fascinate” her with tales of his research, and invites him out to dinner to talk more about it. When she kisses him after their meal, he starts to worry that he is going to have to prostitute himself to get money for his research.

However, Mrs. Latham lets him know that she would have donated the money whether or not he accepted her advances, and he ends up sleeping with her, getting greeted by Penny on his way home the next day with a “Good morning, slut.”

9. Neil deGrasse Tyson, The Apology Insufficiency (Season 4, Episode 7)

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Sheldon walks in on Tyson talking with Raj in the hallways at Cal Tech, ribbing him for being responsible for the demotion of Pluto from planetary status. Tyson defends himself, saying that the demotion was actually done via a vote from the International Astronomical Unit.

“If ifs and buts were candy and nuts we’d all have a merry Christmas,” Sheldon replies, leaving Tyson to ask Raj if that’s “the guy you were telling me about.” Tyson later comes back to Sheldon and apologies for his role in getting Pluto de-planeted, to which Sheldon replies “oh, shut up” and walks off.

8. Steve Wozniak, The Cruciferous Vegetable Amplification (Season 4, Episode 2)

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Co-founder of Apple Computers Steve Wozniak (who Sheldon calls “the great and powerful Woz”) appeared as himself for an episode, as a patron at The Cheesecake Factory where Penny works. The gang is incredibly excited to see him, even Penny, who says that she knows who he is from Dancing With The Stars.

Sheldon, joining the gang via a TV screen, decides that he “must” speak to Wozniak, calling him his 15th favorite technological visionary. “Only 15th?” replies Wozniak. “It’s still six spots above Steve Jobs,” Sheldon replies. Sheldon later rushes over to the restaurant to get Wozniak to sign his vintage Apple II computer, falling down the stairs of his apartment along the way.

7. Stan Lee, The Excelsior Acquisition (Season 3, Episode 16)

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Lee appeared as himself for an episode of the show, doing a signing at Stuart’s comic store as a favor to Stuart’s uncle, his dermatologist. Leonard, Howard and Raj are all able to attend (and even end up getting gelato with Lee), but Sheldon has to miss it to appear in court for running a red light while taking Penny to the hospital for a dislocated shoulder in an earlier episode.

Penny, feeling guilty for making Sheldon miss the signing, takes Sheldon to Lee’s house, where he takes a sarcastic invite to come watch the Laker’s game as serious. Sheldon winds up with a restraining order from Lee, which he hangs up next to his restraining order from Leonard Nimoy.

6. Eliza Dushku, The Apology Insufficiency (Season 4, Episode 7)

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The Buffy the Vampire Slayer and Dollhouse star used her badass acting skills in TBBT as well, appearing in one episode as the FBI agent tasked with doing a background check on Howard when he is trying to be a part of the team building the Defense Department’s laser-equipped surveillance satellite.

Page has to deal with a lot from the gang, including Raj repeatedly telling her about how he is in the country legally and Leonard hitting on her, only to learn that she is actually married to a 6 foot 2 Navy Seal. Sheldon ends up sealing the deal against Howard’s security clearance by revealing the fact that he crashed the Mars Rover because he was trying to get a girl to like him.

Fun fact: Raj is reading New Moon, from the Twilight series, when Page first knocks on his door. This is a reference to Dushku’s role in the vampire-centric Buffy.

5. Summer Glau, The Terminator Decoupling (Season 2, Episode 17)

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Firefly and Terminator: The Sarah Connor Chronicles star Summer Glau appeared as herself, a fellow passenger on the train with the gang as they head to San Francisco for a conference. After Howard questions what Summer Glau would be doing on a train, Leonard says that, “Maybe John Connor is on board and she’s protecting him from an evil Terminator.” Sheldon says its unlikely, and that she might be a Terminator from the future being send back in time by Skynet, disguised as a Terminator actor to infiltrate society.

Howard decides to hit on her, using the 11 hour ride to get her used to the “acquired taste that is Howard Wolowitz.” Howard hesitates to go talk to her, working on the delivery of his opening line, “It’s hot in here, it must be Summer.” Raj takes advantage of his hesitation, sneaking in (after a quick trip to the bar) to talk to her about Slumdog Millionaire, which he says is “loosely based on my life.”

After Howard realizes that Raj is actually drinking non-alcoholic beer and is only able to talk to Glau because of the placebo effect, he swoops in to talk to her about his creepy ice skating dreams and the German roots of the word ‘pumpernickel.’ When Glau says there’s no way of this conversation ending up with the two of them together, Howard agrees to leave, but only after asking if he can take a picture of the two of them together where it looks like they’re making out, resulting in “Terminator” breaking his phone. Leonard also tries his hand at hitting on her, but loses out when she gets off the train in Santa Barbara.

4. Octavia Spencer, The Euclid Alternative (Season 2, Episode 5)

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Octavia Spencer made the guest star rounds before her big break in The Help, appearing in a small part on The Big Bang Theory as a DMV worker when Sheldon finally goes in to get his license after being forced to start driving himself to work (when Leonard starts working nights at the university).

Octavia doesn’t have time to deal with Sheldon’s silly questions about the use of “car length” as a standard of measurement or rants about coefficients of static friction, telling him to “Look at that sign up there. Does it say I give a damn?” When he won’t stop asking questions, she just gives him his learner’s permit without taking the test, telling him to go away.

3. Charlie Sheen, The Griffin Equivalency (Season 2, Episode 4)

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Before he started “winning,” fellow Chuck Lorre-actor Charlie Sheen appeared on TBBT as himself, knocking Raj down a peg when he won’t stop bragging about his People Magazine spread for the discovery of the planetary body trans-Neptunian object 2008 NQ17.

Raj runs into Sheen at The Cheesecake Factory, where he had been out to dinner with the gang, talking up the spread and asking them to come to a party being hosted by the magazine. When they all turn him down, Penny agrees to go with him, and he starts boasting about how he got a date with her, causing the rest of the gang to ditch him. After he starts bragging to other people at the bar about the article, Sheen turns around, telling him to “call me when you’re on the cover.”

2. Katee Sackhoff, The Vengeance Formulation (Season 3, Episode 9) and The Hot Troll Deviation (Season 4, Episode 4)

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Sackhoff appeared on the series twice, both times as a part of Howard’s sexual fantasies. She first appeared in the third season episode in which Howard, nervous about his relationship with Bernadette, fantasizes about Sackhoff while in the bathtub. She tells him that he should commit to Bernadette, because Bernadette is real and Sackhoff is just a fantasy.

She later appeared again in Howard’s bed, dressed in her Battlestar Galactica uniform, before the two are interrupted by the screaming of Howard’s mother. Sackhoff quickly turns into Bernadette, making Howard realize that he still has a crush on her. She later encourages Howard through he and Bernadette’s car make-out session, but takes it a little too far for Bernadette.

1. LeVar Burton, The Toast Derivation (Season 4, Episode 17), The Habitation Configuration (Season 6, Episode 7) and The Champagne Reflection (Season 8, Episode 10)

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Burton also guest starred as himself, appearing three times throughout the series. In the first episode, he is invited to Sheldon’s apartment via Twitter, but winds up getting there after Sheldon has already left, walking in on Barry, Zack and Stuart singing “Walking on Sunshine.” “Oh, I don’t think so,” he says, quickly leaving the apartment.

He later appeared as a guest on Sheldon’s show, Fun with Flags, helping him and Amy discuss Star Trek flags. “Surprisingly, it only took gas money and the promise of free food to get him here,” says Sheldon.

In his most recent guest appearance, he once again appeared as a guest on Fun with Flags, schooling Sheldon on his racist ways after seeing his George Washington Carver impression. Sheldon ends up showing up at his house, causing Burton to lament about how he should have taken Wil Wheaton’s advice and gotten a gate.

Bonus: Leonard Nimoy, The Transporter Malfunction (Season 5, Episode 20)

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Although Nimoy is mentioned frequently on The Big Bang Theory, most people don’t know that the Spock actor actually guest-starred on the show once, lending his voice to Sheldon’s Spock action-figure. The action figure plays the role of Sheldon’s conscience, as it originally belonged to Leonard and Sheldon stole it from him after breaking his own.

Nimoy declined to appear on the show in person, although this fit with the plot of the show, in which Nimoy has a restraining order against Sheldon. The reason for the restraining order has never been revealed on the show.

Nimoy’s guest appearance was one of his last acting credits before his death in February of 2015.