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The original idea for the show was going to focus on four characters, with Phoebe (Lisa Kudrow) and Chandler (Matthew Perry) in supporting roles. In the early stages, the creators toyed with the idea of Chandler being gay, but they changed their minds when they met Matthew Perry. They did, however, insert many jokes about Chandler having gay mannerisms (loving show tunes, etc.).
Joey was originally written as a jerk. When Matt LeBlanc questioned why the others would be friends with him, the character was changed.
When Matt LeBlanc auditioned for the role of Joey, he had eleven dollars to his name. When the cast got their first paychecks, the first thing that LeBlanc bought was a hot dinner. Courteney Cox bought a car.
When Courteney Cox dressed as fat Monica for the first time, Matthew Perry walked right past her without recognizing her.
Courteney Cox was originally supposed to play Rachel. In Friends: The Reunion (2021), she explained that she asked to play Monica instead, since she related to her more.
Lisa Kudrow and her best friend wrote "Smelly Cat" one night when they were drunk, and it eventually got written into the show.