Beyond the core six, "Friends" welcomed many guest stars as part of hilarious storylines.
"Friends" had an impressive 10-season run from 1994 until 2004. The main cast members were Jennifer Aniston as Rachel Green, Lisa Kudrow as Phoebe Buffay, David Schwimmer as Ross Geller, Courteney Cox as Monica Geller, Matt LeBlanc as Joey Tribbiani and the late Matthew Perry as Chandler Bing.
Certain guest stars on the show like, Paul Rudd as Mike Hannigan, Elliott Gould as Jack Geller, Tom Selleck as Dr. Richard Burke, Jon Favreau as Pete Becker, Cole Sprouse as Ben Geller, Aisha Tyler as Charlie Wheeler and Anna Faris as Erica had more extended runs. Others had shorter, yet still memorable appearances.
Below are 25 guest stars you may have forgotten were on "Friends."
Julia Roberts guest starred as Susie, an actress and former classmate of Chandler's in the episode "The One After the Super Bowl: Part 2."
Susie brings up an embarrassing moment Chandler put her through in grade school, which they both casually laugh off, making it seem like she was over the incident.
Susie asks Chandler out, seemingly sincerely, but has other plans in mind.
Christina Applegate plays one of Rachel's sisters, Amy, in two "Friends" episodes.
Applegate first emerged as the stuck-up sister in "The One with Rachel's Other Sister" and a second time in "The One Where Rachel's Sister Babysits."
Reese Witherspoon also plays a sister of Rachel's. She plays Jill in "The One with Rachel's Sister."
Jill ends up having a fling with Ross, after his relationship with Rachel.
Billy Crystal and Robin Williams weren't supposed to guest star in "Friends." It was simply a case of right place, right time.
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Crystal and Williams happened to be in the area during the filming of an episode titled "The One with the Ultimate Fighting Champion," according to Screenrant. The writers asked the duo if they wanted to be in a scene, and they agreed.
Crystal and Williams were in the opening scene of the episode set in Central Perk. Monica begins to tell a story, but is interrupted by a conversation happening between Crystal and Williams. The entire conversation was improvised.
Williams' character begins to tell a story about his wife sleeping with another man. He is shocked when he finds out Crystal's character is the man she has been sleeping with. After the story, the two storm out of the coffee house.
Dakota Fanning is a young child in the episode of "Friends" she guest starred in.
Fanning plays a young girl named Mackenzie who lives in the house Monica and Chandler are moving into.
In the episode "The One with Princess Consuela," Monica and Chandler take Joey to their new home. At the time, Joey is struggling with the couple's move out of the city.
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Joey stumbles upon Mackenzie, who is sad about moving out of the home.
Gabrielle Union plays Kristen Lang in the episode "The One with the Cheap Wedding Dress."
While Monica, Phoebe and Rachel fight off other shoppers for a discounted wedding dress, another plot ensues between Joey, Ross and Kristen.
Kristen moves into the neighborhood and bumps into Joey and Ross at different times, who both ask her out.
Once they find out they are going out with the same women, they decide to let her choose who she wants to be with in a hilarious dating battle.
In "The One with Monica and Chandler's Wedding: Part 1," Joey is in a movie with a famous actor named Richard Crosby, played by Gary Oldman.
The actor has interesting acting techniques, like excessively spitting as he says his lines.
Oldman is also in "The One with Monica and Chandler's Wedding: Part 2," when he almost inadvertently makes Joey miss Monica and Chandler's wedding when he shows up to set heavily intoxicated.
Brad Pitt guest stars in one of the Thanksgiving-themed episodes of the show, "The One with the Rumor."
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Monica invites Pitt's character Will, a former classmate, to dinner after finding out he's spending the holiday in the city with nowhere to go.
This episode reveals a high school secret and a rumor Ross and Will formulated about Rachel back in high school.
Winona Ryder plays a former college sorority sister of Rachel's in "The One with Rachel's Big Kiss."
Rachel tells the group that she and Melissa (Ryder) kissed in college, a story Phoebe refuses to believe as true.
Many "Friends" fans have considered Ryder's appearance in the show to create a plot hole, since the actress is referred to in a prior episode.
George Clooney and Noah Wyle play doctors in "The One with Two Parts: Part 2."
In this episode, Rachel wants to go on a double date with the doctors, a proposition Monica resists, since she was secretly dating Chandler at the time.
Many guest stars have played Phoebe's boyfriend leading up to her eventual marriage to Hannigan (Paul Rudd).
One of these boyfriends is Ryan, played by Charlie Sheen in "The One with the Chicken Pox."
Jennifer Cooldige appears as Amanda Buffamonteezi, an obnoxious former friend of Phoebe and Monica's in the episode "The One with Ross's Tan."
In the episode, she tries to make plans with Phoebe and Monica, who make up excuses as to why they can't meet her, until they eventually find themselves out of reasons.
Bruce Willis' multiple episode appearance has confused some "Friends" fans, since the famous actor is mentioned prior to his guest appearance.
In a handful of "Friends" episodes, the "Die Hard" franchise starring Willis is mentioned as a favorite movie of characters Ross, Chandler and Joey.
In an episode airing after Willis' appearances called "The One Where They're Up All Night," Chandler talks about "Armageddon" while in bed with Monica, another movie starring the famous actor.
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Willis appears in three "Friends" episodes as Paul Stevens, the father of Elizabeth. Elizabeth is the much younger girlfriend of Ross, who he met when she was a student in his class.
During Phoebe's bridal shower thrown by Monica and Rachel, the elegant event takes a turn when the girls find out that Phoebe wanted a stripper at the event. This is where Danny DeVito comes in.
Ellen Pompeo is another guest star in this episode as Missy Goldberg, a former college crush shared by Chandler and Ross.
Freddie Prinze Jr. plays the oversensitive nanny to Ross and Rachel's baby, Emma.
He plays Sandy in the episode of "The One with the Male Nanny."
In "The One with Christmas in Tusla," Chandler is stuck in Oklahoma, away from the rest of his friends in NYC for the holidays.
Selma Blair plays Wendy in the episode, who is also in the office with Chandler for Christmas.
Christine Taylor plays Bonnie, who dates Ross, for three episodes of "Friends." The main episode she is in is titled "The One at the Beach," but she also has appearances in "The One with the Ultimate Fighting Champion" and "The One with the Jellyfish."
Leah Remini is briefly in the episode "The One with the Birth." The main premise of this episode is that Carol and Ross are having their baby.
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In a side plot, Joey meets Lydia (Remini), a soon-to-be single mom at the hospital. When she goes into labor, Joey ends up coaching her through the birth.
Tommy is a character played by Ben Stiller in the episode "The One with the Screamer."
In the episode, Rachel very briefly dates Tommy in an attempt to make Ross jealous. Tommy has a frequent habit of yelling.
Brooke Shields plays Erika in "The One After the Super Bowl: Part 1." In the episode, Shields' character is a crazed fan of Dr. Drake Ramoray in "Days of Our Lives," who is played by Joey.
Throughout this episode, Erika cannot decipher reality from TV fiction.
Sean Penn guest stars in the episode "The One with the Halloween Party" as the fiancé of Phoebe's twin sister Ursula.
Penn sticks around for one more episode, after his character breaks things off with Ursula after learning that she lied about who she was, and dates Phoebe for a short time.
John Stamos appears in an awkward dinner conversation with Monica and Chandler.
Stamos plays Zack, a co-worker of Chandler's in the episode "The One with the Donor."
After finding out they can't have kids of their own, Monica and Chandler consider a sperm donor. This leads them to a strange line of questioning for Zack over dinner, who they see as a potential sperm donor.
Alec Baldwin plays the overly optimistic boyfriend of Phoebe in "The One with the Tea Leaves" and "The One In Massapequa."
He is mostly in "The One In Massapequa," where he accompanies the friends to an anniversary party for Ross and Monica's parents.
In three episodes of "Friends," Dermot Mulroney plays Gavin Mitchell, a character who takes over Rachel's responsibilities at work while she is on maternity leave.
While they begin as rivals, their relationship very briefly turns romantic.
Jeff Goldblum is in the episode "The One with the Mugging," where he plays Leonard Hayes, a director for whom Joey auditions.
