The X-Files is one of the most defining TV shows of the 1990s. For nearly a decade, viewers flocked to their televisions every week to see the latest investigations of FBI agents Fox Mulder and Dana Scully as they delve into all manner of bizarre and disturbing cases. A major part of the show’s appeal is how it spanned across multiple genres; while most episodes had a sci-fi/thriller bent, some of them were more lighthearted and humorous, while others were straight-up horror. However, what really made the show come together was its leads; Mulder’s eagerness to believe in the existence of the supernatural and otherworldly perfectly contrasted with Scully’s pragmatic skepticism.

But Mulder and Scully also had an amazing supporting cast. Eagle-eyed audiences may be surprised to see that there were actually quite a few celebrities who shared the screen with the FBI agents. Let’s take a look at some of the best The X-Files cameos you forgot about.

Tony Shalhoub – “Soft Light” (Season 2, Episode 23)

In this episode, Mulder and Scully look into a case involving people who have been burned to death without any apparent cause. Their investigation leads them to physicist Dr. Chester Banton, who may be the culprit; Well, sort of. He claims that his shadow has taken on a malevolent life of its own when an experiment involving dark matter went wrong and is disintegrating victims.

Tony Shalhoub, best known for his roles in Galaxy Quest, Monk, and The Marvelous Mrs. Maisel shines as the nervous physicist who, for good reason, is afraid of his own shadow. So many of the eccentric quirks that would typify his later characters are on full display here and fit perfectly into the mysterious world of The X-Files.

Kathy Griffin – “Fight Club” (Season 7, Episode 20)

Mulder and Scully’s latest case takes them to Kansas City, Kansas to delve into a mystery involving a woman and her twin. However, these two women are more than just identical twins, but apparently doppelgängers, and it seems that whenever the two of them are close enough to each other, they accidentally wreak all manner of mayhem around them.

Kathy Griffin plays the two twins, Betty Templeton and Lulu Pfeiffer. Griffin’s overly enthusiastic personality steals the show in numerous scenes, but she doesn’t quite have the acting chops to play two different personalities, which somewhat undermines what could’ve been a fun “monster of the week” episode.

Lucy Lawless – “Nothing Important Happened Today” (Season 9, Episodes 1 & 2)

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This two-part episode deals with a secret government program involving the creation of enhanced people. One of those experiments is Shannon McMahon, a former Justice Department employee who was turned into a “super soldier.” However, she’s gone rogue and plans to expose the clandestine scheme, which involved pouring a mutation-inducing chemical into the water supply.

Lucy Lawless – best known for Xena: Warrior Princess as well as her recurring roles on Spartacus: Blood and Sand and Parks and Recreation – stars as Shannon McMahon. She’s perfect for the role, having already proven herself as a tough-as-nails type who still manages to be charming and charismatic.

Shia LaBeouf – “The Goldberg Variation” (Season 7, Episode 6)

Henry Weems, the subject of Mulder and Scully’s latest case, is a man who experiences unusually good luck while causing bad luck to those around him. He uses his good luck to win an illegal poker game against a mobster, with the intent to use the winnings to cover the cost of a liver transplant for a young boy named Richie Lupone.

And that sick little boy was played by Shia LaBeouf in one of his earliest acting roles. Despite his young age, Shia gave a pretty sincere, naturalistic performance that exudes heart without ever getting too sappy.

Octavia Spencer – “Millennium” (Season 7, Episode 4)

This episode ties into the TV series, Millennium, offering a conclusion to the story of the sister series created by X-Files creator Chris Carter. Here, Mulder and Scully are assigned to a case involving a secret society that’s trying to bring about the apocalypse by resurrecting the dead. To prevent the end of the world from taking place at the dawn of the new century, Mulder and Scully reach out to criminal profiler Frank Black (Lance Henriksen) for help.

This is the shortest appearance by a famous actor; Octavia Spencer, who is the recipient of an Academy Award (along with two additional nominations) and a Golden Globe, has a blink-and-you’ll-miss-it cameo as a nurse named…Nurse Octavia.

Ryan Reynolds – “Syzygy” (Season 3, Episode 13)

Comity, New Hampshire may seem like a quaint little town, but as Agents Mulder and Scully dig deeper, they stumble upon a series of bizarre murders of teenagers. The suspects are two high school girls Terri Roberts and Margi Kleinjan, who’ve acquired mysterious abilities from an extremely rare planet alignment.

The teens’ latest victim is the arrogant jock Jay “Boom” DeBoom, who Ryan Reynolds was born to play. Even at this early stage in his acting career, you can see the seeds of the wit, confidence, and charm that he’d become renowned for.

Bryan Cranston – “Drive” (Season 6, Episode 2)

Agents Mulder and Scully are on assignment in Buhl, Idaho, only to get caught up on an even weirder case involving a man named Patrick Crump who the authorities are after. Next thing you know, Mulder is driving a car at high speed with Crump in the back seat – Crump is showing signs of a mysterious illness and believes if Mulder slows down, he’ll die and potentially take Mulder with him.

Bryan Cranston stars as Crump, putting in a wonderfully manic yet tragic performance of a man whose life depends on him constantly moving. If that sounds familiar, it’s because those very same emotional dimensions were what landed Cranston the role of Walter White in the hit series, Breaking Bad. In fact, Vince Gilligan wrote this episode and was so impressed with Cranston that he kept him in mind for when he created the iconic series.