Broad Types of Aliens

From Gurps Space

Dominant
One or more species may dominate others; their power may be military (conquerors or peace keepers) or economic (manufacturers, traders, or explorers). Dominant alien civilizations are well known near their regions of space. The opposite is subordinate species that are dominated by others. Humans are often a dominant species.

Common
A race that is older, fast-breeding, or aggressive in exploration may be encountered often. Such races are also well-known in their localities, regardless of dominance. The opposite is rare; such races may be new to interstellar civilization, secretive, or slow-breeding.

Exotic
Races may be well-known because they have odd customs, bizarre reputations, unusual biology, or control of a particular technology.

Advanced
Some races might have a higher tech level than the rest of the campaign setting- possibly even so advanced as to seem like gods compared to everyone else. They may use their power to help "lesser" civilizations, or to conquer and oppress them. The opposite is primitive, a race that is technologically backward.

Pit Falls to Believable Aliens

by Jedion357

Pit Fall #1 Pets In Space
Basically animal headed aliens. It's a common type and even has been done well, the Orions from David Weber and Steve White's Star Fire novels or the Deng from the Bolo series come to mind. The difference between a pet in space alien in a novel and an RPG is that the novelist has the whole book to develop and bring the alien to life while a typical RPG rule book has two pages on the alien. You probably could get away with a pet in space alien if the culture and background were well developed and inspired people to play that alien.

Pit Fall #2 Humans in Funny Suits
Basically its a really weird looking alien that acts just like a human, has human culture, and or attitudes. A common version of this is to use a recognizable human culture stuffed into the suit. You could probably get away with this if the human culture you were copying was more obscure or less recognizable. In Avatar the Navi totally come off as Native Americans in culture and action. If the culture had been built on the model of an ancient horse culture from Anatolia which might only be recognized by the archaeologist and researchers that worked on it then it would have been less apparent that the culture was simply a copy of a human culture.

Pit Fall #3 Fantasy Escapees
Basically this is taking a staple fantasy race and recasting it in a science fiction setting: dwarves, orcs, elves, etc have been famously done in this way by WH 40K. That is not to say that fantasy games cant be a source of inspiration as I've leafed through a monster manual to find really alien looking beasts to port over to a science fiction game. There are quite a few creatures depicted in the 4.0 monster manual that have tentacles and could easily be from the same ecosystem that the sathar evolved from. One fantasy escapee that worked well was the 40K Necrons; which were basically skeletons recast as soulless robots bent on killing but then the Terminator movies popularized that so Games Workshop got a leg up on that one.  I think you could get away with this pit fall through carefully choosing the fantasy escapee that you use and more likely limit it to a beast on a new planet and not a sapient race.

Pit Fall #4 Just to Weird for ME
The problem here is that if the race is too weird or different that most people will ignore it as they cant wrap their head around the concept. The Osakar of Zebs Guide fell into this pit fall. To a certain degree people have to identify with it if they are going to play it.

Pit Fall #5 The "Star Fish" Alien Concept.
The problem with making something too alien is that players can no longer integrate the alien into the setting as a playable character or npc. For example, what use for space travel would an aquatic ameoboid alien have. If they had any technology that we recognized as technology it probably wouldn't work in a way that functioned with game mechanic rules for firearm combat, space travel, or mechanical technology. That doesn't mean that a back story couldn't be used to explain how this intelligent sentient spieces was given technology by another space faring race that allowed them to interact with our world. It just makes it more difficult to use such an alien right out of the box.