John Lithgow auditioned to be Frasier on Cheers, Rosie O'Donnell tried out to be Elaine on Seinfeld, and more.
Top of the Rock, an oral history of NBC by the former entertainment division president Warren Littlefield, includes all sorts of details from the network's storied history: Seinfeld was initially panned by test audiences. Executives worried at first that Will and Grace would offend advertisers. Shelley Long was difficult to get along with on the set of Cheers. But the most interesting tidbits involve what didn't happen: stories about famous actors who tried out for now-iconic roles on shows like Friends, Mad About You, ER, and more. Here's a look at how NBC's famed Must See TV shows might have looked a lot different: