9. Carol Willick - Friends
Friends introduced Ross' (David Schwimmer) ex-wife Carol in the show's second-ever episode, "The One With The Sonogram At The End," where she was played by Anita Barone.
Yet Barone, who originally auditioned for one of the lead roles, quit the part after just a single appearance because she wanted to pursue other leading parts.
As such, Barone was replaced with Jane Sibbett for Carol's remaining appearances across the series.
It's an especially interesting switch because not only did Sibett bear just a superficial resemblance to Barone at best, but her depiction of the character was also markedly different.
Though we naturally got only a sketch of Carol 1.0 as played by Barone, Sibbett's portrayal was drier and far more sarcastic, and absolutely for the better. But because the switch happened so early in the show's history, many fans didn't even notice.