The final film featuring the original cast of Star Trek exists because of a fortunate coincidence. At the turn of the final decade of the 20th Century, the Cold War between the United States and the Soviet Union came to an end. Star Trek VI: The Undiscovered Country was able to end the original cast's era with one final allegory casting the Federation as America and the Klingons as the USSR. However, if director Nicholas Meyer had been able to get his first choice for the Starfleet villain, Saavik (with Kirstie Alley reprising her role), the film would've been heartbreaking.
Source：https://www.cbr.com/saavik-star-trek-6-tragic-villain/
