“kafka” answered in the June 2010 issue:
Their history and psychology. Trying to find ways to under populate the Traveller Universe is easy with so many rock balls generated during planetary generation. However, coming up with credible alien sophonts is the more challenging parts of Traveller therefore, I have usually opted for the approach of no more than 1 per subsector (roll die 1-3 on a d10) assuming the world has a biosphere capable of supporting life.
To avoid, a Star Wars or D&D Monster Manual approach, I usually keep the alien races in the background usually on reservations oppressed by the Imperium or the Imperium clustered in a few key city arcologies. A useful way of looking it, of course, is the same as District 9, save that the Imperium will reinforce the apartheid of aliens and humans. Notwithstanding, there are societies that are more integrated and less integrated. Determining as I said the history and their relationship to the Imperium is the first task. Then working to figure out a unique psychology that makes them “alien” which is conformity with the history then becomes easy. Figuring out how physiology and environmental considerations also play into the equation is the next step.
So, therefore, I may have very few “mainstream Imperial” the ones that I do have will have a story directly linked to the adventure that I might be running that particular game session.
Other ways that I have made them interesting is the classic Doctor Who or Star Trek method...which is present the race as an enigma. Be they technologically advanced - hence almost “magical” or believably “primitive” but in their rites and rituals illustrate that either they were once technologically superior or were in contact with a technologically superior culture. And, often, it requires the PCs or one NPC to have gone native to figure out the puzzle for success in the adventure.
“Travis” answered in the July 2010 issue:
An alien race, or monster, is made interesting by the common motivations they act from. What makes them different from humans? We are achievement oriented by and large, but what about a race with a hive mind, or maybe a splinter of humanity where communism actually worked? Stats and physical differences aren’t really that interesting.
Paul Anuni answered in the March/April 2020 issue:
I think this question applies even to so-called “mainstream Imperial” humans; Traveller doesn’t really seem to have a “default culture” unless it’s an implicit (and somewhat derided) ‘Yanks in Space’. In any case, the answer comes down to world-building—if a society feels “real”, like you’ve walked into something that’s existed for a long time, and isn’t just a ‘set’ for your characters and the NPCs to act in front of, the world-building has been done well, and is more likely to be interesting. Specific aspects that attract my interest typically involve discovering how the society portrayed differs from my own (so-called “middle America”)—sure, it’s ‘easier’ to play if my own assumptions about behavior hold true Far Away And In The Future, but why would I want to be a Traveller in such an environment? I’d want to go where Things And People Are Different, so that I could explore the local culture, and in the process perhaps learn more about myself.