Shows That Had An Almost Completely Different Cast By The Time They Ended

Though "Grey's Anatomy" has since blown past it, "ER" was once the longest running primetime medical drama of all time in the U.S. — and at 15 seasons, its second place position seems pretty well-secured. Debuting on NBC in 1994, the initial main cast was a mix of relatively new faces along with several veterans of both the big and small screen. At the time, Anthony Edwards was probably the most recognizable name and face in the cast, having previously starred in "Top Gun" and "Revenge of the Nerds," though George Clooney would eventually stake his claim as the most famous member of the show's first lineup by a considerable margin.

Along with Clooney and Edwards, the actors that comprised the main cast when "ER" first started were Sherry Stringfield, Noah Wyle, Eriq La Salle, and Julianna Margulies. Stringfield was the first to exit at the end of Season 3, with subsequent cast members dropping out at various points until Wyle was the final original actor to leave, after Season 12. The regulars of the last few seasons consisted of Maura Tierney, Linda Cardellini, Scott Grimes, John Stamos, David Lyons, and Angela Bassett, with none having been on the show any earlier than Season 6. All of the originals, however, did make guest appearances throughout the final season.