When the original Star Trek debuted a half-century ago on Sept. 8, 1966, it was to middling reviews. But, even though that earliest iteration would only last three seasons, there were some who saw that the show was more than just the average sci-fi adventure. And those prescient fans included one very important person in particular.

It’s a story that has since become legend within Star Trek circles: after the first season, Nichelle Nichols, who played Uhura in the original series, decided to leave the show for a role on Broadway. As she would later recall, creator Gene Roddenberry asked her to think about the decision over the weekend before officially quitting. That very weekend, she was at a fundraiser when one of the staffers told her that her “biggest fan” was “desperate” to meet her. She graciously agreed to say hello to the fan.

That fan was none other than Martin Luther King Jr.

Star Trek was, he said, the only show he allowed his children to stay up late to watch. When she told him that she was planning to leave the show, he told her that she just couldn’t: though African-Americans were making great strides toward equality, she represented one of the only examples of that equality on American television. Uhura was intelligent and beautiful and commanding and, he pointed out, a role that wasn’t specifically the role for a black woman. Her presence on that space ship showed the world that a black woman could be all of those things.

Nichols, of course, decided to stay on the show.

That special Star Trek quality was very intentional: the show’s creator Gene Roddenberry specifically envisioned a better future in which the strife that marked the real world had been overcome. “The show had an idealistic, ’60s counterculture mind-set, imagining a 23rd-century world in which humans had outgrown war and prejudice,” as Richard Zoglin explained in the recent TIME special edition about the show.

Get your history fix in one place: sign up for the weekly TIME History newsletter

As Roddenberry put it in the 1968 book The Making of Star Trek:

Intolerance in the 23rd Century? Improbable! If man survives that long, he will have learned to take a delight in the essential differences between men and between cultures. He will learn that differences in ideas and attitudes are a delight, part of life’s exciting variety, not something to fear. It’s a manifestation of the greatness that God, or whatever it is, gave us.

It’s a tradition that continued with the latest iteration, the movie Star Trek Beyond. “The whole point of any Star Trek exercise,” wrote TIME’s critic Stephanie Zacharek, “is that people of different temperaments, beliefs and skin tones must learn to work together.”

Get our History Newsletter. Put today's news in context and see highlights from the archives. Please enter a valid email address. Sign Up Now Check the box if you do not wish to receive promotional offers via email from TIME. You can unsubscribe at any time. By signing up you are agreeing to our Terms of Use and Privacy Policy . This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Thank you! For your security, we've sent a confirmation email to the address you entered. Click the link to confirm your subscription and begin receiving our newsletters. If you don't get the confirmation within 10 minutes, please check your spam folder.

Write to Lily Rothman at lily.rothman@time.com.