I was surprisingly moved upon learning of Nimoy's death. Why should that be? He wasn't a second-degree relative or co-worker, but that's how my subconscious must feel about him.
I think it must be because things that he's done have been particularly meaningful to me from firsthand watching (or listening), and similar effects on others have left traces that can be seen on many things in our current culture at large and SF-fans/futurists/engineers in particular.
The fact that I know some of these off the top of my head, and will happily give an analysis on demand to those who seem to be missing the depth of appreciation, indicates that Nimoy's traces run throughout my mind and have been incorporated into things I've learned. In that way, it is like an uncle who spends time with a child during formative years, so odd random things (like seeing a kid flying a kite when driving by the park) can pull on those threads.
Now for some specifics: Adam Link. Do you know the name? How about I, Robot. In this usage that it a short story published in 1938 (January magazine comes in December).
If you Google that tile, you will be hard pressed to find that usage of the title unless you add “Adam Link” to the search. According to his autobiography, when the publisher told Isaac Asimov that they were changing the title of his short story collection from Flesh and Metal (Ah, now the cover makes sense!) to I, Robot, he said “No! That's the name of a story by Otto Binder” to which Campbell (?) replied “So?”. As it turns out the story was inspirational to Asimov who took the theme as his own and developed it substantially, and helped make a sea change in the public's perception of robots (monsters --> tools).
I digress — somewhat, perhaps. This serves to further illustrate the interconnected web of influences and the relay-race of imagination. The public at large did not know about serious literary science fiction; just B movies which in this case helped fuel the trope of Robot as the 20th century's Frankenstein's Monster. They didn't read Amazing Stories, but in 1964 they certainly watched TV! And they saw Leonard Nimoy (known as a guest star in more than 50 TV shows before that) play a reporter who (representing the audience as first person learning of the events) discovers that Adam Link is a thinking, feeling, kind and selfless being, not a monster. And even as he gives his life to save a child, people are prejudiced against him because of what he is. The story revolves around Adam being blamed for a death for no reason other than being close at hand. It was an allegory for the civil rights movement, which is an example of “Golden Age” SF used to reflect on real issues by changing the particulars and allowing the reader to see the situation without triggering his existing emotional attachment to the real version.
Knowing all this, in the 80's seeing a factory with industrial robots and some human workers on an assembly line was the "kid flying a kite", evoking Isaac Asimov, Eando Binder, and Leonard Nimoy. I think I only knew who the actor was because of Star Trek, which is an interesting retro-influence.
Retro influence — now there's a twist. After Nimoy became a Big Star, people would look up his older works or notice when he appeared in some old rerun, and pay attention to the themes of the older work. In 1979 the allegory of 1964 was rather transparent, and that might prompt people to realize how literary SF (as opposed to most popular movies) could be a thoughtful reflection on real issues. And then Enemy Mine wins a Hugo. That's more true than ever today, with on-demand and easy access to many old works, a fan can look up what some favorite actor/author/artist did in the past and be exposed exactly when he's in the mood to pay attention to it.
And then in 1995, Nimoy played in I, Robot again. I was attracted to the new series because they teleplays inspired by many great SF stories. So I saw Leonard Nimoy play Adam Link's defense attorney. In this telling, the theme was about the effects of advancing technology on humanity. Most people were attracted to the show not because of the writers but because of the overt “star power” of the cast. People knew the famous actor Leonard “Spock” Nimoy and payed attention to him playing, not a stoic alien, but a lawyer of all things, struggling with his own prejudices. Nimoy had played cowboys, spies, supervilians, and just about everything else long before Spock, but young audiences in 1995 knew none of that.
Here we have an interesting symmetry, where the fame of Mr. Spock leads new audiences to Adam Link in both the past and the future.
In both Adam Link teleplays, Nimoy, in different roles, leads the audience through the emotional ride, revealing internal conflicts and growth that provide the real punch of the play, with the overt events being merely backdrop. The dry facts, were we to watch them as 3rd person, is a simple sequence of events. The simplicity is key. Nimoy shows us the 1st person reaction to the events, without being a participant.
It's a George Burns script: in outline, “Cutler is conflicted. Cutler shows internal reflection.” Making the SF killer robot story into an allegory of man's prejudices, fears, and growth lies in the skill of the actor. A simple set showing a bare prison cell with a humanoid robot sitting still — sounds like a boring play — but the camera pushes in and the action is on Nimoy's face.
We see that good lasting stories are part of a web of influences that draw from common culture and then become part of it for later efforts. But the question is specifically about how Acting/Characterization contributes creatively like a wordsmith, and in a written work the author would indeed have to do all that himself). At its simplest, the actor fleshes out the "Burns Lines" and somehow conveys emotions or unspoken body language that the word-only writer indicated. Nimoy did that here, allowing the play to be about the person's reactions, rather than what any props, set-dressing, and action scenes would do. In some cases (like The Night Thoreau Spent in Jail) the inner action is wordy and overtly scripted as a written work. In showing feelings, the actor has to figure out how to physically convey that through body language, posture, facial expression, tone of voice, etc. That body-script is probably not written down at all, and may best be spontaneous. The author saves a lot of work by not writing a two-page eloquent soliloquy and instead just states "Nimoy has a revelation" and leaves him to make that contribution.
Ah, that's obviously human drama, but how's that worldbuilding? Well, yea. The human drama exists because of something happening in the outer world, and that something could be a love triangle, car wreck, or revolution, society changing discovery, change to moral landscape, or anything that may be an allegory to real-world events. Applying it to strange unfamiliar SF stuff is harder and can make the strange world more believable and sell it to the audience.
And that's not even Star Trek. :)