One of Roddenberry's ideas for the show originally was that a woman should be second in command of the Starship USS Yorktown (as the spacecraft was provisionally named).
Majel Barrett was duly cast in the role for the 1964 pilot episode, 'The Cage'. This didn't go down well with the NBC studio executives who already thought the pilot was too cerebral and felt that the show would go over the heads of most of the audience.
They also didn't like the alien, Mr. Spock because he looked too much like the devil and would alienate the many religious groups in the US !. Finally, the idea of a female first officer was considered too radical by far. Roddenberry sought a compromise: he'd write out the female number one if NBC let him keep Mr. Spock. The network reluctantly agreed, on condition that 'the Devil-like alien' was kept in the background. Ironically, when Roddenberry later introduced the strong female role of Communications Officer Lt. Uhura (Nichelle Nichols), she became one of the show's most popular characters.
Gene had wanted very much to show women in a more positive point of view, and women that were stronger, because he said they exist in the world - but he kind of pulled back a little and said ''Okay, they are pretty things'', and that's why we end up with little short skirts and big bouffant hairdos and, you know, it was a very sexist thing to do, but he did it.
Robert F. Justman, Joint Producer, Star Trek Original Series
Gene Roddenberry would drop everything he was doing when it came time to approve a costume, especially if it was a costume on a female. He had an eye for the ladies; it didn't matter what it was - a story conference, cutting a film, the daily rushes - whatever, he would stop and he would immediately proceed to make it better, and by making it better, one means making it more revealing and less voluminous.
Inevitably, the emphasis changed from women as powerful, knowledgeable figures of authority to women as foxy fodder for Kirk's amorous attentions. For a lot of people who first watched Star Trek at an impressionable age, their over-riding memory of the show is of knee-high boots and sensational costumes.
Jonathan Ross, Television Presenter
Part of the appeal was that there is alien life out there which is basically almost all humanoid, and we can chat to, and occasionally fight, and occasionally get on with, but the idea of sex with aliens... The idea that you could have a girlfriend who had maybe yellow skin and purple hair, or blue skin and green hair, or was just blonde but wore fantastic go-go dancer outfits... That was what I loved about the women in Star Trek, they all dressed like they'd just come from either a strip-joint or a go-go dancing club. The hair teased up, big fake eyelashes (aliens are obviously big on fake eyelashes), and they'd all fall for Kirk! For many years I did effect the slightly boyish Kirk quiff, in the hope that I would finally meet someone from Alpha Centuri who would fall for me, but it still hasn't happened.