As our faithful chronicler reminds, S3:E5 of Star Trek: TOS was first broadcast this day in 1968 with the return of actor Diana Muldaur in the franchise, this time as psychologist Dr Miranda Jones—whom would later portray medical officer Katherine Pulaski on the Enterprise as the second season replacement for Dr Crusher, who was brought back for the third season (casting producers were unaware of Muldaur’s previous roles when McFadden was written out of the script—see also here and here) accompanying Medusan ambassador Kollos (transported around in a cooler) and the crew assigned to escort the two to a rendezvous point with a Medusan star cruiser. The non-humanoid aliens described as so repulsive, their outward appearance leads to death by insanity, though Spock may observe the ombudsman by shielding a direct gaze with a visor, as can Jones, crediting it to Vulcan like mental discipline from living among them and psychic abilities.
Spock and Jones collaborate throughout the mission to first return to known space and then save the science officer’s sanity when he catches a glimpse of Kollos unfiltered. During the denouement, Spock appears in Starfleet dress uniform as they greet the Medusan delegation, featuring a medallion that represents Vulcan philosophy, prompting Jones to ask during the formal function if that badge was a subtle note that he as a Vulcan could mind-meld with the Medusans far better than she could. Spock replied to the contrary, that it represented, “The glory of creation is in its infinite diversity—and the ways our difference combine to create meaning and beauty,” pinning the medal on Jones to honour her achievements and skill. The speech was controversial and disliked by cast members who saw the exchange as a merchandising ploy for Roddenberry to see replicas of the IDIC badge through the mail-order memorabilia company Lincoln Enterprises (see also) run by his Roddenberry’s wife, Majel Barrett—which is precisely what it was. The slogan’s next appearance was in the TAS episode The Infinite Vulcan and has since become canonical and a motto for inclusiveness.