2. Gary Seven
A name not known to many outside of established Trek fandom, Gary Seven appeared in only one episode of the Original Series, Assignment: Earth. When the crew of the Enterprise travel back in time to 1968 they meet this advanced stranger who, along with his cat, just happens to be agent working for an alien race, keeping an eye on humanity to make sure we don't blow ourselves up (have I already mentioned how the series would be relevant?). Including Gary Seven in the show would be a no brainer, as it comes with too many positives it could add to the series. Firstly, as a human working on behalf of an alien agency, and someone equipped with everything from a super computer to a transporter, Gary Seven would add an extra element of Science Fiction that a series based on Star Trek just wouldn't work without. Genetic experiments aside, you could only include so much advanced human technology before straying outside of established Star Trek lore, and including actual aliens would just make the whole series unbelievable; Gary Seven is a perfect compromise. More than this, like Khan himself, Gary Seven simply deserves more screen time due to the fact that he is a fantastic character in his own right. Plans were even made for Seven to have his own spin-off series (his episode was produced when Star Trek was on the brink of cancellation), but these ultimately never came to fruition. Including him here would not only give fans their chance to catch up with another much loved character, but also given them a closer glimpse at one of Roddenberry's undeveloped projects.