Davis appeared in a 2000 episode of Friends, playing a woman who dates Joey (Matt LeBlanc) and then befriends Rachel and Phoebe (Lisa Kudrow), who want the two to share more of a connection than they actually have. As Davis explains, being on Sex and the City at the time didn't help ease her nerves about working on Friends. "Sex and the City was in production, but I was nervous to be the tiny character of Erin, losing sleep, partly because of the live audience, but partly because you’re in this world that has been created that is so alive and so specific and you’re trying to make sure you’re fitting yourself in there properly," she told TODAY.

Hollywood is a small town, and while Aniston was a relative newcomer when Friends began, the rest of the Central Perk gang happened to have history with many of the actors hired for smaller roles. Applegate had worked onscreen with Matthew Perry and LeBlanc and knew Cox and Kudrow, while Davis had gotten to know the group through the Sex and the City cast doing award show circuits alongside Friends.

Mitchell Whitfield played Rachel's orthodontist fiancé Barry, who she ditched at the altar in the pilot episode. He appeared in several episodes during the show's early years, but as he recalled in his TODAY interview, he could have become one of the titular Friends. "Originally I was brought in by the producers to be considered for Ross (Schwimmer)," Whitfield explained. "And then they met with me and I read for them a couple times and it was being considered for Ross and for Chandler... I got a phone call from someone early on from the show saying, 'Congratulations, you're gonna play Ross.'"

Of course, that casting choice fell through, but because of how strong David Schwimmer was as the character, Whitfield never felt weird about how things panned out. "Because of my consideration for the other parts, that's how Barry ended up coming about," he said.

This Season 1 episode proved that some of the series' strongest stories were the ones with only the six main characters together. Davis was working on a Season 1 episode of E.R. at the time, and the medical drama filmed on a sound stage near the Friends set. One day, Davis and E.R. star George Clooney spent their lunch break watching the Friends cast tape this episode.

"We sat up in the stands and watched them rehearse and it was so funny and amazing," she said. "They were so on it in terms of their voices and their characters and the beats, and they just knew what they were doing, and I remember being blown away by their confidence level and their synergy as a group."

Season 2 of Friends began soon after Rachel learned of Ross' feelings for her and realized she reciprocated them. But Ross returned from a lengthy fossil dig with a new girlfriend, Julie (Lauren Tom). The first half of the season focused on Rachel's jealousy of Julie, and Tom revealed in her TODAY talk that fans watching the show's live tapings were always intensely on board with Ross and Rachel being a couple.

"I wasn't prepared for the amount of venom I was about to receive in a live audience where they actually booed my character,” she said. “And, of course, I was trying very hard not to get my feelings hurt. So I had to get used to that. But I did understand intellectually that, you know, the audience was meant to be rooting for Rachel. Even I was rooting for Rachel, on some level, because I was a fan of the show."

When Ross' ex-wife Carol first appeared on the series, a different actress played her, but starting in Carol's second episode, Jane Sibbett portrayed the lesbian character who fell in love with Susan (Jessica Hecht) soon before learning she was pregnant with Ross' baby. The three co-parented Ross and Carol's son Ben throughout the series, but in a Season 4 episode, Ross' insecurity about Susan hanging out in London with his current girlfriend spread to Carol. The two had nothing to worry about, but Susan obviously loved life in London, and according to Sibbett, the city plays a part in the present-day life she and Hecht imagine for Carol and Susan.

"Jess and I decided that Carol and Susan would be over in London, that Ben would be just getting out of college and we'd be stalking him unmercifully to make sure that he was doing the right thing," the actor told TODAY.

Before he was a mischievous twin living at the Tipton Hotel, Sprouse appeared as Ben from 2000 to 2002. While most of his scenes were with onscreen dad Schwimmer, Sprouse acted opposite Aniston in an episode where Ben and Rachel bonded over practical jokes. The story stood out to Sprouse for leading to the set-wide reveal of his feelings for Aniston.

"I'm pretty sure I fell in love with Jennifer Aniston, which the whole world had at that point," he told TODAY. "I remember blanking on my lines, and having a kind of stage fright when she sat next to me on the couch in one episode. And I remember there was a camera man who was like, ‘Little boy's got a crush' ... Of course, I turned bright red. But I do remember feeling like I fell in love.”

Rachel met Italian beau Paolo during a city blackout in Season 1, prompting intense jealousy from a pining Ross. While Paolo delivered romantic-sounding Italian phrases toward Rachel, Fusco was actually told to say whatever he liked in Italian for his first appearance. "When I'm standing by the window with Jennifer, and I say, ‘Look at the moon, look at the stars,’ I just said that and it stayed in everyone's mind," he revealed.

Nowadays, you'll find plenty of online articles about how Ross Geller is actually the worst, but the actors TODAY spoke to particularly raved about Schwimmer, who directed the episode in which Davis starred. She called him "a great director," while Sibbett praised Schwimmer for his work in the pilot episode and a scene they later shared in "TOW The Candy Hearts." Hecht and Fusco also loved working with the star, and Hecht told TODAY, "He's really smart about bits. Like, he understood how to make all the funny stuff more funny, and how to set it up."

Many of the actors' stories from the Friends set involved witnessing the friendship among the six stars, but Tom's memory of the group is especially sweet. "They were very bonded. When I started, it was the point at which they were just taking off like a rocket ship," she said. "Sometimes I think that even a success can feel like a crisis, because it's so huge. And so they kind of really clung onto each other. They would literally walk down the set on Warner Brothers arm-in-arm."