NBC’s beloved bar comedy did a superb job of replacing Diane with Rebecca and Coach with Woody, but its greatest addition might have been the pompous psychiatrist played by Kelsey Grammer, who joined the cast in Season 3 as Diane’s therapist/boyfriend.

Diane left, but Frasier stuck around, acting as the stuffy intellectual counterweight to the beer-swilling Cheers gang — and he even landed his own spinoff, "Frasier", which ran for 11 seasons of its own.

https://tvline.com/lists/best-tv-characters-late-cast-additions-seinfeld-buffy-the-office/best-tv-characters-late-cast-additions-frasier-crane-cheers/