Before they were Emmy nominees, superhero movie headliners, or ultra-recognizable character actors with resumes a mile long, many an aspiring star cut their teeth on a little show called "The X-Files."
The saga of FBI agents Fox Mulder and Dana Scully, an unlikely team united in the knowledge that the truth is out there, "The X-Files" was a groundbreaking series for its time, and fertile guest-spot ground for some of today's biggest celebs before they were household names. Below, we round up 54 of the best people ever to make us yell, "Hey, it's that guy!" while re-watching the best alien conspiracy series ever to define the 1990s.
1. Giovanni Ribisi
Before he drilled for unobtainium in "Avatar," Ribisi played a human with the lightning bolt-throwing powers of Zeus in Season 3 episode "D.P.O." Bonus cameo: Jack Black co-starred in the same episode as one of the unlucky electrocuted.
2. Bruce Campbell
The star of the "Evil Dead" series turned up in a Monster of the Week standalone episode as a demon who desperately wanted to be a father.
3. Michael Emerson
Before he creeped us out as "LOST" villain Benjamin Linus, Emerson starred in the second-to-last "X-Files" episode ever as a man with psychokinetic abilities and a bizarre fixation on "The Brady Bunch."
4. Jodie Foster
You won't see her onscreen, but Foster's disembodied voice features prominently in "Never Again," an episode in which a man believes his tattoo is telling him to commit murders.
5. Doug Hutchison
The producers of "The X-Files" liked the "Green Mile" actor (and erstwhile husband of Courtney Stodden) so much in the role of a liver-eating mutant who could squeeze through air vents, they asked him to do it twice.
6. Felicity Huffman
In a guest role during the show's first season, the "Desperate Housewives" actress had the privilege of being infected with rage-inducing parasitic worms -- twice!
7. Brad Dourif
Before he leered grossly at Eowyn in "Lord of the Rings: The Two Towers," the man who played Wormtongue appeared as a death row inmate who claimed to be able to contact Scully's dead father.
8. Zeljko Ivanek
Best known as "that guy who was in that thing," Ivanek (who's appeared in everything from "Heroes" to "True Blood" to "Argo") gave a surprisingly sweet performance as a developmentally disabled man possessed by the murderous genius spirit of his cryogenically frozen twin brother.
9. Tony Todd
Shortly after horrifying us as an evil ghost full of bees in "Candyman," Todd showed up on "The X-Files" in the equally-creepy role of a Vietnam vet out to kill the men who made him physically unable to sleep ever, ever again.
10. CCH Pounder
You know her from "Sons of Anarchy," "The Shield," and "The Mortal Instruments," but long before that, Pounder played a no-nonsense FBI agent on a case involving alien abduction.
11. Mark Rolston
The same year that he skeeved out audiences everywhere as the creepiest prison rapist in Shawshank, Rolston also appeared on "The X-Files" as a cult leader with terrible taste in turbans.
12. Terry O'Quinn
The "LOST" star (and his long-gone mustache) appeared multiple times on "The X-Files" -- first as a smalltown police seargeant, and twice later as a shadowy member of the NSA.
13. Michael J. Anderson
The backward-speaking Man from Another Place played a snarky sideshow owner in the Edgar-nominated "Humbug." The episode also featured real-life professional freaks The Enigma and Jim Rose, as well as renowned character actor Vincent Schiavelli.
14. Tony Shalhoub
Before he was "Monk," Shalhoub starred in the episode "Soft Light" as a man whose shadow could kill.
15. John Neville
Neville made many "X-Files" appearances as a character known only as The Well-Manicured Man, but we'll always know him (and GIF him) from his lead role in the criminally underrated "The Adventures of Baron Munchausen".
16. Peter Boyle
The actor who became famous for playing a singing, dancing Frankenstein's monster also put on the ritz in "Clyde Bruckman's Final Repose" as a morose psychic who foresees an intimate end for himself and Scully.
17. J.T. Walsh
The actor who excels at playing sleazy middle-aged bureaucrats was in good, albeit familiar, form on "The X-Files" as a pompous prison warden.
18. Jewel Staite
Years before her iconic turn on Joss Whedon's space Western, the "Firefly" actress turned up on "The X-Files" as a teenage kidnapping victim in episode "Oubliette."
19. Kevin Zegers
Back before he was a world-class hottie, Kevin was a teeny tiny stigmatic in an episode centered on Scully's Catholic faith.
20. Michael Berryman
Appearing in the same episode as Kevin Zegers, the peculiar-looking Berryman took a break from playing monsters, madmen, and mutants to take a role as a saintly protector.
21. R. Lee Ermey
And in the same episode as Berryman and Zegers, the famous "Full Metal Jacket" drill sergeant put his expert shouting skills to use as a loudmouthed fire-and-brimstone preacher.
22. Ryan Reynolds
This chubby, tear-stained kid? Yep: It's Ryan, pre-beefcake era, about to be murdered by a pair of psychically connected teenage girls.
23. B.D. Wong
Before he played a good-hearted forensic psychologist on "Law & Order: SVU," Wong was a bad cop with a worse haircut on "The X-Files."
24. Lucy Liu
And in the same episode as B.D. Wong, you'll see a then-unknown Lucy Liu in a teeny tiny guest spot!
25. Jesse Ventura
He may not have time to bleed, but Ventura managed to carve out a moment in his busy schedule to play a Man in Black in the stellar episode, "Jose Chung's From Outer Space."
26. Alex Trebek
And you probably didn't know this, but when he's not hosting "Jeopardy!", Alex Trebek is a black-suited alien conspiracist, too.
27. Laurie Holden
The "Walking Dead" actress played Marita Covarrubias, an agent of the powerful shadow government group the Syndicate, in a 10-episode run over the course of two seasons.
28. Richard Belzer
In a wild collision of franchises, Belzer's character John Munch from "Homicide: Life on the Street" and "Law & Order: SVU" crossed over to "The X-Files" for a single episode in 1997.
29. Katharine Isabelle
The Canadian scream queen and star of the "Ginger Snaps" franchise cut her teeth on supernatural fare with a role in "Schizogeny," a.k.a. the episode with the killer trees.
30. Luke Wilson
No "X-Files" cameo is more famous than Wilson's in "Bad Blood", in which he played a local sheriff who may or may not have had a terrible overbite.
31. Patrick Renna
Also in "Bad Blood": the redheaded kid from "The Sandlot" as an obsessive-compulsive vampire.
32. Lili Taylor
Taylor, who starred in 2013 horror hit "The Conjuring," made a rare TV appearance during "The X-Files" fifth season because she liked the show so much.
33. Ed Asner
Famous for playing a crotchety Santa Claus in "Elf" and voicing an even more crotchety senior citizen in "Up," Asner starred in a rare Christmas episode of "The X-Files" as a ghostly old man with a hole in his head. Bonus: Lily Tomlin played his wife.
34. Jesse L. Martin
In "The Unnatural," the first episode of the show to be directed by David Duchovny, Martin plays a baseball-loving alien-in-disguise in 1947 New Mexico, which is just as weird and great as it sounds.
35. Mark Pellegrino
In keeping with his usual preference for playing a narrow-eyed sleaze, Pellegrino appeared in episode "Hungry" as a nebbishy aspiring blackmailer named Derwood Spinks.
36. Shia LaBeouf
Long before he hid from plagiarism accusations inside a paper bag, Shia played a sweet little boy with liver problems in episode "The Goldberg Variation."
37. Willie Garson
Appearing alongside Shia LaBeouf was Garson, best known as Carrie Bradshaw's GBF Stanford Blatch on "Sex and the City."
38. Anthony Heald
Best known for creeping on Clarice Starling as asylum administrator Frederick Chilton in "Silence of the Lambs," Heald turned up in the show's seventh season as a police psychic named Diller. (This GIF of Heald chewing sassily on a pen is not from his "X-Files" appearance, sadly.)
39. Garry Shandling and Tea Leoni
In "Hollywood A.D.", an episode written by David Duchovny, Leoni (then Duchovny's wife) and Shandling played fictionalized versions of Scully and Mulder in a movie-within-the-show... if that makes any sense.
40. Minnie Driver and David Alan Grier (not pictured)
In the same episode, Driver and Grier -- who had just finished making the romantic comedy "Return to Me" along with Duchovny -- stopped by to make uncredited cameos as audience members attending the screening of the movie-within-the-show.
41. Kathy Griffin
The comedienne appeared in a dual role as identical twins in episode "Fight Club." Two, two, two Griffins in one!
42. Eddie Kaye Thomas
Before he slept with Stifler's mom in "American Pie," Thomas was abducted and murdered by aliens in a season seven episode of "The X-Files."
43. Danny Trejo
Go-to bad guy Trejo did his usual thing in episode "Redrum," playing an assassin.
44. Joe Morton
In the same episode, "Terminator 2" actor Morton stars as a man experiencing time backwards in the aftermath of his wife's murder.
45. Adam Baldwin
Favorite of Joss Whedon and star of "Firefly" and "Serenity," Baldwin had a recurring "X-Files" role as Rohrer, an alien hybrid supersoldier who was part of the Syndicate conspiracy.
46. Lucy Lawless
The warrior princess played opposite Baldwin (and ultimately fought him to the death!) as another supersoldier.
47. Cary Elwes
Nothing will ever top Elwes's swoony role in "The Princess Bride," but his appearances as Brad Follmer throughout the ninth season of "The X-Files" were nevertheless appreciated.
48. Bryan Cranston
Cranston famously won his starring role on "Breaking Bad" after impressing Vince Gilligan with his sympathetic portrayal of a deranged bigot in Season 6 episode "Drive."
49. Dean Norris
Fellow "Breaking Bad" star Norris appeared in "F. Emasculata," a Season 2 episode of the show in which exploding pustules figured heavily.
50. Aaron Paul
Aaron was clearly getting practice for the part of Jesse Pinkman when he guested on episode "Lord of the Flies," as seen in this video of he and his friends auditioning for a reality TV series called "Dumbass." (Funny, that sounds familiar.)
51. Jane Lynch
Appearing in the same episode as Aaron Paul, Lynch's pre-"Glee" turn on the Fox network saw her playing the role of a giant insect-person who could spew webbing from her mouth.
52. Neal McDonough
You know him as the burly Dum Dum Dugan from "Captain America," but back in 2002, McDonough had a two-episode arc as an FBI agent in possession of a magical alien healing device (which comes in handy, for obvious reasons.)
53. Beth Grant
Before she doubted your commitment to Sparkle Motion, "Donnie Darko" actress Beth Grant played a crazy snake-handling church lady on "The X-Files."
54. Michael McKean
Of all the celebs ever to guest star on "The X-Files," Christopher Guest favorite Micheal McKean is the best -- because without him, this GIF would not exist.