Tools of Characterization
Characterization in Star Trek: The Motion Picture
Speech and Dialogue
In Star Trek: The Motion Picture, our heroes do a whole bunch of talking. It is a Star Trek movie, after all.
For example, Spock is defined by his incessant stream of philosophical musings, exposing the internal struggle between his passionate human side and logical Vulcan side.
Check out a representative example:
SPOCK: V'Ger has knowledge that spans this universe. And, yet, with all this pure logic, V'Ger is barren, cold—no mystery, no beauty. I should have known.
On the other side of the spectrum is Bones McCoy. Bones isn't interested in philosophical lollygagging or metaphysical experimentation—he only cares about what's right in front of him in the here and now. This down-to-earth perspective provides a nice contrast to Spock. Check out this great one sentence shut-down:
SPOCK: What it requires of its god, Doctor, is the answer to its question, Is there nothing more?
McCOY: What more is there than the universe, Spock?
In a single conversation, we see the differences between Spock and Bones placed into high relief. Nice.
Type of Being
This is Star Trek we're talking about, so you shouldn't be surprised that one's species is used as a powerful tool of characterization.
One example is Spock. As a half-human, half-Vulcan, Spock's torn between two diametrically opposed poles: the cold hard logic of Vulcan society and the passionate emotionality of humanity. This conflict has always been a part of Spock's character, but we see it amped up massively by the entrance of V'Ger.
Speaking of V'Ger, did you forget that thing's a giant living machine? That's pretty awesome. It also raises some interesting questions about the nature of technology, making us question everything from the way we talk to Siri on our iPhones to the way we play video games. In addition, V'Ger's mechanical nature leads it to have a coldly logical disposition that distinguishes it from the film's other characters.
Actions
The differences between Captains Kirk and Decker are never more apparent than when they're at the helm of the Enterprise.
Kirk has a tendency to throw caution to the wind. For example, he orders Scotty to engage the ship's warp drive despite being within the solar system (which is dangerous) and dealing with some serious engine malfunctions (which is super dangerous). In a similar way, he fearlessly pushes into the heart of V'Ger even when Decker is telling him to hold back and lick his wounds.
Decker's style can be summarized as such: always be cautious. He frequently tells Kirk to stop taking so many risks with the crew and even ends up saving the Enterprise's butt by countermanding Kirk's order to fire phasers inside a wormhole.
Still, Decker proves himself to be a pretty fearless dude by the end of the movie, especially after sacrificing himself to merge with V'Ger and save the Earth.