2) Star Trek
From one juggernaut of sci-fi television to another, Star Trek has endured across the decades through various incarnations. However, its success can be traced back to the original 60s show, with its two leads in William Shatner’s Captain Kirk and Leonard Nimoy as his logical first mate Spock. In the original pilot, however, neither character was the same.
First of all, the big thing is that Kirk was nowhere to be seen. The lead in the pilot is Captain Christopher Pike, as played by Jeffrey Hunter. When Star Trek went to series, however, Hunter elected not to return. Shatner was then drafted in and a new character was created for him.
Moreover, Pike’s second-in-command was Number One, as played by Majel Barrett. However, the network didn’t like putting a woman at the forefront of the show. As such, Nimoy’s supporting character was bumped up to fill in her role.