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Jack Shephard (Matthew Fox), Lost
As originally scripted, Jack was supposed to die halfway through the pilot, as a signal that the audience should always expect the unexpected from the show. But fearing that the viewers would resent the show for killing off a seemingly major character so quickly, the script was rewritten. (Fun fact: Producers were interested in Michael Keaton for the role, but he who turned down once the role was meant to continue on in the series.) Instead, Matthew Fox's Jack became the Oceanic 815 survivors' de facto leader and the show's main protagonist.