4. Joanna McCoy
D.C. Fontana had an idea to expand the back story of Leonard McCoy by introducing his daughter Joanna as a character in the series. There were two attempts to bring her into the fold, first in the episode Joanna which ended up being significantly rewritten until it became The Way to Eden. The original version would have seen a romantic interest between Joanna McCoy and Kirk (of course), which leads to a conformation between the Captain and the Doctor. Such was the expectation that Joanna McCoy was going to appear that she's mentioned in Gene Roddenberry and Stephen E. Whitfield's The Making of Star Trek as a character who was going to be appearing shortly the book was written prior to season three of The Original Series. The second attempt, entitled The Stars of Sargasso, was intended for the fourth season of The Original Series but was cancelled along with the rest of that season. She's subsequently appeared in the novelisations, comic books and even a mention in an Animated Series episode but nothing canon.