Tools of Characterization
Characterization in Alien
Actions
The actors in Alien are pros, so some of the best indicators we have of characterization come from their actions.
Take Ripley. Although Dallas is technically the captain, Ripley's actions show who the true leader is aboard the Nostromo. She doesn't let the away party aboard the ship due to potential contamination—totally the right move, by the way—and she takes charge once Dallas has had his date with the alien destiny.
Lambert, on the other hand, tends to be a more emotional, crying a lot and becoming frantic when she or other members of the crew are in danger. You could write her off as a weak woman, especially compared to Ripley's willingness to action, but we think of her as empathetic. Her fear is the type of fear we can all relate to, and she can likewise relate to the fear of those around her.
Finally, let's consider Ash. Eventually we learn that Ash is a robot sent to protect the company's interests in the alien. But even before he loses his head over the issue (ba dum tiss) Ian Holms makes odd mouth moments from time-to-time and quirky gestures like that time he runs in place. It is as though he's not quite comfortable in his own skin. Small though they are, these actions tell us something just isn't quite right about this guy.
Speech and Dialogue
Speech and dialogue can also help us understand these characters. Say what??
Consider Kane and Lambert. While investigating the planetoid, Kane, Lambert and Dallas come across an alien spaceship. Lambert suggests they book it, but Kane says, "We've come this far. We have to go on." (Alien). Obviously, Kane is the more adventurous and curious of the two. We directly see evidence of this later. Kane is the one who climbs the wall to find the "Space Jockey," and he's the one who descends into the hatchery. And did we mention him actually touching the egg?
Then there are Brett and Parker. Every time Parker says something, Brett responds with a smile and utters "Right." In that single word, we clearly understand that Brett's not the kind of person to rock the boat or let the boat tip over. He is clearly the more submissive of the two engineers.
Parker, by far the more aggressive and passionate of the two, uses a lot of exclamations. He yells, "What the hell are you doing, man?" at Brett for not catching Jonesy. To which Brett, perfectly in character, responds, "It's the cat, man."
Social Status
We're using the term "social status" a bit loosely here, but there's definitely a pecking order aboard the Nostromo. Parker and Brett are at the bottom as engineers while the other characters are at the top as officers. Think of it as Marxism Lite—all the class relations and social conflict but with half the calories.
Parker resents this more than Brett and likes to complain about how they don't come down to his part of the ship or how Brett and he deserve equal shares. He's hostile to the others, especially Ripley, and Ripley has to pull out her no-nonsense card. Consider this exchange:
Parker: Hey, Ripley, I want to ask you a question. If they find what they're looking for, does that mean we get full shares?
Ripley: Don't worry, Parker. Yeah. You'll get whatever's coming to you.
Brett: Look, I'm not going to do any more work till we get this straightened out.
How the characters align and interact here is based on this class structure. Brett and Parker stand on one side of the hallway, Ripley on the other. They don't share the frame together because they don't share points of view on the issue of shares.
Even when the alien is picking them off one at a time, Parker and Ripley maintain a hostile relationship. Parker wants to kill the alien without talk, but Ripley pulls rank on him. Ultimately, the class barriers between Ripley and Parker break down when they finally agree to blow up the ship and kill the alien. It seems that survival trumps class when it comes to alien invaders aboard your spaceship.