If you’re going to make a television series about future versions of diverse Earth folk living in harmony and equality, you have to portray said Earth folk living in harmony and equality. Star Trek’s (1966) central cast spoke to this central mission. Even though the main trio: Kirk (William Shatner), Spock (Leonard Nimoy) and Bones (DeForest Kelley) were, for all intents and purposes, three white guys, the crew that accompanied them "where no man had gone before" was anything but standard American television fare during the 1960s.
Consider how revolutionary it was in the 1960, during the height of Cold War tensions, for the fictional galactic spaceship The Enterprise to bring on a Russian-born crewman on board as navigator. Anton Chekov (Walter Koenig) was a radical character idea that spoke directly to contemporary international relations and politics, offering hope for future unity.
Similarly, Lieutenant Uhura (Nichelle Nichols), the ship’s communications officer was a black woman, the likes of which had never been seen in mainstream television. Having a woman in such an important (and non-stereotypical) position of power broke the mold; her dark skin color got the whole world talking. Star Trek’s socially important commentary proved so profound for its time that even Dr. Martin Luther King Jr. was a fan, and reportedly convinced Nichols to stay with the program when she thought about quitting.
“You are changing the minds of people across the world,” he told her, “because for the first time, through you, we see ourselves and what can be.”
Rounding out the crew was Scottish-born engineer and aptly-named Scotty (James Doohan), as well as Hikaru Sulu (George Takei), the Japanese-American helmsman tasked with piloting the Enterprise. The show frequently served as not-so-subtle allegory of East vs. West conflicts during the Cold War, and employed representatives from those same areas working in unison toward a common goal. It was innovative and optimistic, and raised the bar for television casting.
Star Trek was even progressive behind the scenes, as writer and script editor DC Fontana was one of the handful of female television writers of the time. She went on to pen some of the series’ most notable episodes. Aside from her, the series' writing contributions were all male, save for a few episodes: "The Gamesters of Triskelion" and "The Paradise Syndrome" by Margaret Armen, and "Is There in Truth No Beauty?" and "All Our Yesterdays" by Jean Lisette Aroeste being the exceptions.
All this isn’t to say the show always succeeded in equally depicting different races and the sexes, particularly the latter. In hindsight, the show presented some overtly sexist overtones with regard to many of its storylines and female characters, save for Uhura. Sometimes it was the network’s doing (the series’ original pilot had a female first officer, but NBC didn’t think audiences would connect with that.) Other times it was the script - right, "Mudd's Women?" That episode's story, widely considered one of The Original Series' most abject examples of sexism, centers around three women who essentially can't see any purpose in life but finding a male counterpart and come aboard The Enterprise looking for Mr. Right.
It's also easy to think about "Space Seed," the episode which introced legendary Trek film villain Khan, played by Ricardo Montalban. He managed to seduce Lieutenant McGivers (Madilyn Rhue) so intensely that she's willing to betray all of her Starfleet training and condemn many of her crewmates to death to appease him. It's completely uncharacteristic behavior attributed to a woman, again expressive of the belief that finding a man to be with is more important than anything else. And of course, don't forget about "The Cage," Star Trek's original pilot episode. It featured a green animal woman who lived in a cage and came from a planet where women enjoy being taken advantage of. For real.
Wardrobe-wise, miniskirts, low-cut dresses and hyper-sexualized costumes objectified and sexualized the female form. And dialogue, even from “logical” characters like Mr. Spock, often tended towards sexism. (Staring at a robot in “The Changeling,” Spock says “That unit is defective. Its thinking is chaotic. That unit...is a woman!”)
Still, Star Trek pushed certain important boundaries. It teetered on the edge of acceptability but found clever ways to break new ground - after all, that’s how television’s first scripted interracial kiss came to be in the “Plato’s Stepchildren” episode. Under the guise of telekinetic mind control, Kirk is “forced” to kiss Uhura against his will by the dominant Platonians. Hiding the kiss under the guise of undesirability allowed the show to accomplish something socially radical, the impact of which became legend.
Star Trek was a daring show, with revolutionary casting decisions that helped facilitate its socially progressive commentary. While it seems unbelievable now, the cultural and societal landscape at the time of the show's airing in the 1960s-70s wasn’t accustomed to members of a variety of races shown working together on television. Roddenberry’s vision of the future was a powerful message, and its casting choices were the voice.