Star Trek: The Next Generation launched with several key female characters to star the show through the first few seasons. From Guinan to Dr. Beverly Crusher to Dr. Pulaski, Star Trek has always been able to create such great female characters. Two of the more popular ones from the Next Generation were Deanna Troi and Natasha Yar.
Deanna Troi was played by Marina Sirtis, and Natasha Yar was played by Denise Crosby. Except, that wasn’t always the case. Just days before the shooting of the pilot, Sirtis was set to play Natasha Yar, and Crosby was going to play Deanna Troi.
So why the change?
Well, according to TrekCulture, Yar was originally going to be a character named Lt. Hernandez, a female security officer modeled off of Vazques from Aliens. Sirtis was awarded the role and was set to play the character. Crosby on the other hand was given the role of Deanna Troi.
Just before filming began, the two women were swapped out of their roles for one another. Lt. Hernandez became Natasha Yar, and Sirtis became Deanna Troi. The reasoning for this is that Crosby was better built for the role of a security officer, instead of Sirtis. As Crosby was five to six inches taller than Sirtis and had broader shoulders, that tracks. While equally beautiful, Crosby looked far more like a butt-kicker than Sirtis.
It would’ve been interesting to see a “What If” scenario play out, just one episode, to see how each other would’ve handled the roles. We got to see something of a “What If” scenario already with Crosby’s Yar being killed off at the end of the first season, only to be brought back in a later episode, still alive.
With alternate realities, and different writing mechanics to make such a thing possible, it would’ve been great to get an episode where the two switched duties for some reason as a wink and nod at the original casting assignments.