According to Noah Baumbach at the Lincoln Center anniversary screening, there was another actor scheduled to play the lead role who dropped out at the last minute, prompting Tri-Mark to tell Baumnbach to "find a star" or they'd cancel the movie. He quickly faxed his good friend Eric Stolz, who was filming Rob Roy (1995) in Scotland, and got him to sign on to the movie even though there was no character written for him. They created the character of Chet together, doing a lot of improvisation, in particular the famous "book club" scene.
The trivia item below may give away important plot points.
Elliott Gould's character offers an apartment to Josh Hamilton's character, which he describes as an apartment in Greenwich Village, near a coffee shop. Gould, for years, played Monica and Ross' father on Friends (1994), which takes place in Greenwich Village, near a coffee shop.