18 Epic ‘Big Bang Theory’ Guest Stars from the Worlds of ‘Star Trek,’ ‘Galactica,’ ‘Star Wars,’ More

Over its 12-season run, The Big Bang Theory evolved into one of television’s great pop-culture crossroads. What began as a comedy about nerdy and brilliant but socially awkward scientists gradually turned into a series that attracted icons from science, film, television, sports and fandom itself. And crucially, these guest appearances were rarely gimmicks. Instead, they were woven directly into the show’s world, often poking fun at celebrity, hero worship, and the characters’ own obsessions with franchises like Star Trek, Lord of the Rings, Star Wars and Battlestar Galactica.

From legendary actors and filmmakers to Nobel-level scientists and real-world heroes, Big Bang found a way to make each appearance feel earned. Whether it was a dream encounter, a fantasy come to life or a perfectly timed reality check, these moments underscored what the series was designed to be: a celebration of curiosity, enthusiasm, and unapologetic fandom.

The following gallery highlights some of the most memorable guest appearances across the show’s run—from early-season surprises to late-series victory laps—capturing the moments when The Big Bang Theory stepped outside its apartment walls and intersected with the wider cultural universe. Being a geek never felt so good.

1. Sean Astin and Kal Penn

Lord of the Rings icon Sean Astin—yes, Samwise Gamgee himself—turns up on The Big Bang Theory as a cheating potential Nobel Prize winner in “The Laureate Accumulation,” joined by Kal Penn in a Season 12 episode that rattles Sheldon to his core. (Season 12, Episode 18, aired April 4, 2019)

2. Adam Nimoy

Adam Nimoy, son of Star Trek legend Leonard Nimoy, appears on The Big Bang Theory in “The Spock Resonance,” interviewing Sheldon (Jim Parsons) for a documentary exploring the cultural impact of Spock. (Season 9, Episode 7, aired November 5, 2015)

3. Billy Bob Thornton

Fresh off roles that defined his offbeat screen persona, Billy Bob Thornton (Sling Blade, Bad Santa) brought quiet menace to The Big Bang Theory as Dr. Oliver Lorvis, matching wits with Sheldon (Jim Parsons) in “The Misinterpretation Agitation.” (Season 8, Episode 7, aired October 30, 2014)

4. Bill Nye and Bob Newhart

Bill Nye the Science Guy and Emmy-winning comedy legend Bob Newhart collide on The Big Bang Theory in “The Proton Displacement,” an episode that turns Sheldon’s lifelong admiration for Professor Proton into an unexpected rivalry. (Season 7, Episode 7, aired November 7, 2013)

5. Buzz Aldrin

Apollo 11 astronaut Buzz Aldrin appears as himself in The Big Bang Theory episode “The Holographic Excitation” (Season 6, Episode 5, aired October 25, 2012), ultimately serving as a mirror to the way that Howard has been behaving.

6. Carrie Fisher and James Earl Jones

Carrie Fisher and James Earl Jones guest star on The Big Bang Theory in “The Convention Conundrum,” bringing Star Wars royalty into Sheldon’s orbit in one of the series’ most celebrated cameos. (Season 7, Episode 14, aired January 30, 2014)

7. George Takei and Katee Sackhoff

Star Trek icon George Takei and Battlestar Galactica favorite Katee Sackhoff collide on The Big Bang Theory in “The Hot Troll Deviation,” blending classic sci-fi royalty with modern genre fandom. (Season 4, Episode 4, aired October 14, 2010)

8. Jerry O’Connell

Best known for Stand by Me and a long career in film and television, Jerry O’Connell makes a memorable Big Bang Theory debut as Sheldon’s long-mentioned brother Georgie in “The Sibling Realignment.” (Season 11, Episode 23, aired May 3, 2018)

9. Joe Manganiello

Joe Manganiello (True Blood) guest stars on The Big Bang Theory in “The D & D Vortex,” bringing his real-life passion for Dungeons & Dragons into the series’ most epic fantasy-themed episode. (Season 12, Episode 16, aired February 21, 2019)

10. Judd Hirsch

Judd Hirsch — the Emmy-winning star of Taxi — guest stars on The Big Bang Theory as Leonard’s father in “The Convergence Convergence,” bringing old-school sitcom gravitas to the Season 9 finale. (Season 9, Episode 24, aired May 12, 2016)

11. Kathy Bates

Kathy Bates—Oscar winner for Misery—brings her unmistakable intensity to The Big Bang Theory in “The Consummation Deviation,” playing Amy’s no-nonsense mother opposite Sheldon. (Season 12, Episode 8, aired November 8, 2018)

12. LeVar Burton

When Sheldon finally meets LeVar Burton — the man behind Reading Rainbow and Geordi La Forge — the result is The Big Bang Theory’s unforgettable episode “The Champagne Reflection.” (Season 8, Episode 10, aired November 20, 2014)

13. Mark Hamill

Mark Hamill — forever Luke Skywalker to generations of fans — guest stars on The Big Bang Theory in “The Bow Tie Asymmetry,” officiating Sheldon and Amy’s wedding. (Season 11, Episode 24, aired May 10, 2018)

14. Teller

Teller of Penn & Teller brings his understated comic presence to The Big Bang Theory in “The Conjugal Configuration,” playing Amy’s soft-spoken father in the Season 12 premiere. (Season 12, Episode 1, aired September 24, 2018)

15. Nathan Fillion

A longtime fan favorite, Nathan Fillion appears on The Big Bang Theory in “The Comic Book Store Regeneration,” fitting seamlessly into the show’s pop-culture-savvy universe. (Season 8, Episode 15, aired February 19, 2015)

16. Professor Stephen Hawking

Renowned physicist Stephen Hawking guest stars on The Big Bang Theory in “The Hawking Excitation,” a landmark moment for both the series and its science-loving audience. (Season 5, Episode 21, aired April 5, 2012)

17. Summer Glau

Summer Glau (Firefly, Terminator: The Sarah Connor Chronicles) appears in “The Terminator Decoupling,” one of The Big Bang Theory’s most memorable early guest-star episodes. (Season 2, aired March 9, 2009)

18. William Shatner

A pop-culture dream table: Wil Wheaton, William Shatner, Johnny Galecki, and Kareem Abdul-Jabbar in The Big Bang Theory’s “The D & D Vortex.” (Season 12, Episode 16, aired February 21, 2019)