The 15 Best Guest Stars On The Big Bang Theory, Ranked

"The Big Bang Theory" shines a spotlight on nerd culture thanks to hilarious storylines and endearing characters that helped shape the careers of Jim Parsons, Melissa Rauch, Simon Helberg, and Kunal Nayyar, just to name a few. While the antics of Sheldon Cooper (Parsons), Howard Wolowitz (Helberg), Raj Koothrappali (Nayyar), and Leonard Hofstadter (Johnny Galecki) already offer plenty of laughs, the show would not be complete without big guest stars.

Many guest stars have solidified their place within the fabric of pop culture, which is important for a show that makes so many references to well-known movies and TV shows. It gives the characters a chance to interact with many of the celebrities that they refer to while making jokes that share details about a person's career. 

In order to rank the best 15 guest stars on "The Big Bang Theory," we reviewed the length of each appearance, how much the guest star adds to the episode's plot, and how much of the dialogue references the person's career. The list starts at the bottom and works its way up to the top. So, without further ado, here are the 15 best guest stars from "The Big Bang Theory."

The second person to walk on the moon during the Apollo 11 mission appears during season 6, episode 5, "The Holographic Excitation." The episode focuses on Howard and his inability to stop sharing moments from his trip to space. The constant astronaut chatter is getting old, and his wife, Bernadette (Melissa Rauch), begs him to tone it down. Howard eventually agrees, and Buzz Aldrin sends the point home. At the end of the episode, Raj sends Howard a video of Aldrin handing out candy on Halloween, but that candy comes with the price of hearing space puns that all loop back to Aldrin's illustrious space career. Howard then vows to cut back on his space talk.

While Aldrin's appearance is very brief and doesn't include any direct interaction with "The Big Bang Theory" cast, it's a moment that nicely concludes the main plot of the episode. Plus, it leaves the audience with a good chuckle.

What happens when you pit Bill Nye against fellow science educator Arthur Jefferies, better known as Professor Proton (Bob Newhart)? It's what Sheldon wants to find out after J ditches him to spend time with Leonard — or at least that's how Sheldon sees it. He becomes friends with Nye during season 7, episode 7, "The Proton Displacement." He hopes that the new friendship will make Arthur jealous, but his plan backfires. Instead, Arthur reacts with rage toward Nye over stealing his ideas, and Nye eventually leaves Sheldon at a smoothie shop. Sheldon is shocked, but his friends use this moment to help him understand that he can be overbearing.

While Nye's appearance does push the plot toward its resolution, much of his dialogue is meant to set up jokes for Arthur, who offers dead-pan jabs at his arch rival. However, that dialogue does make references back to Nye's career that has been focused on breaking down scientific principles so that they can be accessible to kids and adults alike.

Season 4, episode 2, "The Cruciferous Vegetable Amplification," finds Sheldon worrying about his mortality, and he finds that the best way to stay alive is to stay in his apartment while a robotic version of himself roams the outside world. His plan is working perfectly until a lunch with friends turns into a chance encounter with Apple co-founder Steve Wozniak. Sheldon's robotic form races over to the inventor's table. He mentions how much he loves his Apple II, and Wozniak wishes that he could sign it for him. Sheldon then springs out of the apartment and runs down the stairs with his computer. Unfortunately, he takes a tumble, crushing his computer and hurting himself in the process.

Wozniak's appearance is extremely brief, but it helps teach Sheldon that you unfortunately can't protect yourself from everything, no matter how careful you are. There are many moments in life that are just better in-person, and the appearance of the legendary computer genius helps to send the message home.

In every generation there is a Chosen One meant to stand against the vampires, and she was also chosen to sit next to Raj at Amy (Mayim Bialik) and Sheldon's Nobel Prize ceremony. Sarah Michelle Gellar, the face of "Buffy the Vampire Slayer," appears during season 12, episode 24, "The Stockholm Syndrome." The gang is heading to Stockholm, Sweden, and Raj tells everyone that Gellar is on their flight. HIs pals tell him that it's just a lookalike, but he proves them wrong. As Amy and Sheldon give their acceptance speech, Gellar is spotted sitting next to Raj. Sheldon is in shock, and it's a big moment that stemmed from one phone call.

Showrunner Steve Holland told TVLine that the idea of asking Gellar to be on the series finale came about when series co-creator Chuck Lorre suggested that Raj should have a fun seatmate on the plane. Holland said, "[Having Sarah in the finale] felt like a fun, like, deeper-reel pull that would be exciting to us and exciting to the characters." Holland added that they were excited to see Raj enjoying a moment with a celebrity crush.

Kevin Smith is a fixture in pop culture thanks to a comedic catalog that includes the "Clerks" films, "Chasing Amy," and "The 4:30 Movie," which /Film called a refreshing new chapter in his career. So it only makes sense that he would be a part of a podcast recording session with Wil Wheaton on season 8, episode 20, "The Fortification Implementation." Smith's appearance is only a voiceover, but it plays a big role in the episode. He offers Penny (Kaley Cuoco) the chance to read for "Clerks III" after praising her performance in "Serial Ape-ist 2." Leonard reminds Penny that she just got a new job, and he doesn't think that she can juggle two jobs. This turns into a fight that takes over the podcast. While the voiceover helps set up the main plot, it also gives Wheaton and Smith a chance to poke fun at each other's careers. 

The two stars would appear together again on season 12, episode 16, "The D&D Vortex," which finds Smith playing Dungeons & Dragons with other celebrities. While his appearance on that episode doesn't impact the plot as much, he does bring plenty of laughs as he argues with Joe Manganiello about the best way to play.

The actor who played Hikaru Sulu during all three seasons of "Star Trek: The Original Series" gives Howard love advice on "The Big Bang Theory," season 4, episode 4, "The Hot Troll Deviation." George Takei appears in Howard's romantic dream alongside Katee Sackhoff as he struggles in the aftermath of his breakup with Bernadette. Takei begins his appearance by talking about sexual orientation before Sackhoff asks him questions about being typecast as a science fiction icon. They become engrossed in their conversation and leave Howard to face his love for his ex-girlfriend.

He and Sackhoff reappear at the end of the episode as Howard and Bernadette rekindle their romance. Takei encourages him to take it slow, but Howard ignores his advice and starts to take things to the next level when Bernadette confirms that she needs a slower pace. It's a guest appearance that helps usher in a new chapter in Howard and Bernadette's relationship. Plus, his references to "Star Trek" and his personal life make this an enjoyable moment for fans of Takei and Sulu.

Season 3, episode 16, "The Excelsior Acquisition," features the late, great comic book legend Stan Lee. The face of Marvel is heading to Stuart Bloom's (Kevin Sussman) comic book store for a signing, and Sheldon, Howard, Raj, and Leonard are excited to meet him. The only problem is that Sheldon has traffic court the same day, and it's all due to a mistake made by Penny. Sheldon hopes that he can get to the bookstore in time, but a fight with the judge lands him in jail. Penny gets Lee's address and surprises Sheldon with a trip to his home. It's a big surprise for Lee as well, and he wants them to leave immediately.

While Lee's appearance on "The Big Bang Theory" is short, he is a key ingredient in the episode's central plot. Of course, his on-screen moment is highly anticipated, and saving that bit for the end is a nice way to close things out. While his dialogue doesn't mention his Marvel work, he is wearing a blue robe that has the "Fantastic Four" logo on it. He then becomes the newest celebrity to issue a restraining order against Sheldon.

Season 12, episode 16, "The D&D Vortex," captures Captain Kirk playing Dungeons & Dragons with other celebrities, and Sheldon wants in on the action. William Shatner kicks off the episode by talking to Sheldon and Amy on the children's show "Professor Proton," which is now hosted by Wil Wheaton. Sheldon is so excited by Shatner's appearance that he throws up on the actor. He later learns about Wheaton's celebrity D&D night. His friends are begging to join the game, but jealousy enters the narrative when only Leonard is asked to play.

Shatner's appearance is a long-awaited moment for fans. Steve Holland told the New York Post that past attempts at a guest appearance didn't work out, and they were hoping to include him in the final season. "I got on the phone and chatted with him about what we were thinking about for the episode — at that point we didn't have a script — but I think he felt he wanted to be a part of this before it came to an end," said Holland. 

Including Shatner in this episode is a fitting choice given that he is playing D&D with other big names like basketball star Kareem Abdul-Jabbar. His appearance also includes a "Star Trek II: The Wrath of Khan" joke about ogres.

The Force is strong with Sheldon Cooper as he goes on zany adventures with James Earl Jones during season 7, episode 14, "The Convention Conundrum." Their friendship begins when they have lunch to discuss a pop culture convention that Sheldon is creating. Lunch turns into an ice cream outing, a carnival excursion, and a karaoke number inspired by "The Lion King." They even play ding-dong-ditch at Carrie Fisher's house, and she is not happy about Jones' reoccurring prank.

His appearance takes up a good chunk of the episode, and the many references to "Star Wars" and "The Lion King" make this a fun installment for "Star Wars" and Disney fans alike. It was also a big moment for Jones, who met Fisher for the first time ever during this episode.

Jones had many dramatic roles during his career (which sadly ended when he passed away in 2024), and this series of hilarious events that he participates in on "The Big Bang Theory" truly showcase his comedic talent. 

Season 5, episode 21, "The Hawking Excitation," is the moment when one theoretical physicist meets a legend in his field, but Sheldon has to earn his conversation with Stephen Hawking, who passed away in March 2018. Howard is helping Hawking during his visit to Caltech, and he wants to introduce him to Sheldon. When Sheldon makes critical comments toward Howard, he makes him work for the chance to discuss his recent scientific discovery with the scientific genius. After jumping through several hoops, the two finally meet to talk about Sheldon's work, but Hawking points out a mathematical error that makes him faint.

Sheldon's journey to an in-person conversation with Hawking is the basis for this episode. Once we reach his on-camera appearance, his major brain power is on full display thanks to the twist that turns Sheldon's paper from a sudden triumph to a sudden work in progress. This is just one of his many guest appearances on the show, and they were the episodes that Simon Helberg enjoyed the most. While season 5, episode 21 is the only time that viewers see Hawking, audiences can hear his voice in six episodes.

Howard and Bernadette's love blossoms throughout "The Big Bang Theory," and that couldn't happen without the help of Katee Sackhoff, who plays Kara "Starbuck" Thrace on "Battlestar Galactica." The actress first appears during season 3, episode 9, "The Vengeance Formula." Howard is in the bathtub dreaming about the actress amid the early days of his romance with Bernadette, and Sackhoff is wondering why he is spending his night with a fantasy instead of a real woman who loves him. It's a moment that helps put everything into perspective and helps move their relationship in the right direction.

Sackhoff returns on season 4, episode 4, "The Hot Troll Deviation." This time, she is wearing her "Battlestar Galactica" flight suit while confronting Howard amid his breakup with Bernadette. After Howard and Bernadette restart their relationship, Sackhoff is the voice in his head telling him to make bold moves as the two kiss. While her appearances only last a few moments, they make a big impact on the couple's relationship.

Sheldon has a restraining order from Leonard Nimoy. It's a running joke on "The Big Bang Theory." So it is only fitting that his son, Adam Nimoy, would make an appearance, and it's in the spirit of honoring his father, who died at age 83 in February 2015. Season 9, episode 7, "The Spock Resonance," premiered in November of that year, and it follows Adam as he interviews Sheldon for a documentary about his dad. Sheldon shares everything he learned about life from Mr. Spock. However, Penny counters his statements and offers another perspective on why Vulcans suppress their emotions. It all helps Sheldon come to terms with his feelings surrounding his breakup with Amy.

The episode first aired the year before Adam released a real documentary about his father titled "For the Love of Spock." It follows his career and the creation of Spock, including why he was almost cut from "Star Trek: The Original Series." Leonard Nimoy never physically appeared on "The Big Bang Theory," but he does voice a Spock action figure during season 5, episode 20, "The Transporter Malfunction." 

LeVar Burton is a steady presence in pop culture thanks to his moving performance on "Roots," his scene-stealing role on "Star Trek: The Next Generation," and his years teaching kids the joy of reading on "Reading Rainbow" (which has a great documentary out there that's worth watching). So, it is only fitting that he would appear throughout the run of "The Big Bang Theory." 

Burton's first cameo is on season 4, episode 17, "The Toast Derivation." Sheldon is upset that he is not at the center of his friend group. He decides to replace them with new pals and invites Burton to hang out with them. He eventually shows up at the apartment and runs away after walking into a bizarre karaoke night.

He reappears during season 6, episode 7, "The Habitation Configuration," and he is a guest on the web series, "Sheldon Cooper Presents: Fun with Flags." His third and final appearance happens on season 8, episode 10, "The Champagne Reflection," which features Sheldon taping the last episode of his show. He gets Burton to stop by again, but this time, it's under the condition that Sheldon must delete his contact information. His hilarious appearances add extra pizazz while including references to his biggest roles.

Bob Newhart lent his comedic talents to "The Big Bang Theory" for six episodes by playing Arthur Jefferies, also known as children's TV host Professor Proton. He first appears on season 6, episode 22, "The Proton Resurgence," when Sheldon pays him to visit his apartment. He reappears twice during season 7, and that includes episode 22, "The Proton Transmogrification," which chronicles Sheldon's reaction to Jefferies' death. He returns as a ghost and continues to watch over Sheldon until season 12, episode 5, "The Planetarium Collision."

In 2013, Newhart told The Hollywood Reporter that recurring appearances was just one of stipulations that he made as he considered the role. He was also looking for a part that would not require him to do another pilot to series. "'The Big Bang Theory' is well-written and it has an incredible cast. It's intelligent, which is a vanishing commodity," he said. When Newhart passed away in July 2024, co-creator Bill Prady posted a photo of himself with Newhart on his X account (formerly Twitter). The caption read in part, "Working with him ever so briefly was one of the greatest joys and honors of my life."

Wil Wheaton appears 17 times on "The Big Bang Theory." He first walks onto the scene during season 3, episode 5, "The Creepy Candy Coating Corollary," which has Sheldon plotting revenge against him after he didn't appear at the 1995 Dixie Trek Convention as promised. They go head-to-head in a "Mystic Warlords of Ka'a" tournament, and Wheaton says his grandmother died around the time of that convention. This turns out to be a big lie, causing Sheldon to lose the tournament and grow his hatred toward the actor.

The arch nemesis storyline continues as they battle at a bowling alley on season 3, episode 19, "The Wheaton Recurrence." Wheaton even befriends Leonard during season 5, episode 5, "The Russian Rocket Reaction." Their rivalry eventually turns into a friendship, and Wheaton becomes a guest on "Sheldon Cooper Presents: Fun with Flags."

The real Wheaton is different from "The Big Bang Theory" version because he didn't want to actually play himself on the show. It's a move that gives the show room to have fun with his appearances, and it helps to create an entirely new overarching plot for the series.