Synopsis of Encylopedia Galactica entries on the various star races:

Notes:
1) Humaniform - aka Humans, Syreen, Androsynth, Juraians.  Genetically
similar, able to interbreed.
2) Precursors - one of, if not the first sentient race in the universe.
They achieved a level of technology unsurpassed since, but suddenly
disappeared.  It wasn't until recently that it was discovered that the
Precursors "devolved" themselves, seeking to hide from a trio of powerful
forces that they felt would destroy them.  It was later discovered that
these forces were the original higher-dimensional existences of Tokimi,
Tsunami, and Washu (see related notes).  The Precursors have been restored
several times, but demand to be returned to their previous forms, even when
told of the current state of their "bogeywomen".

Power Name: Arilou
Major Race: Ariloulaleelay (Arilou).  All Arilou look alike.  They are 1.5m
tall.  They are very slender and have pale blue skin.  For a comparible
Humaniform race, they appear to be a child in early puberty with an
overlarge head.
Minor Race: None known.  Theories of kidnapped Humaniforms (especially
Humans) have abounded.
Technological Specialization: Spatial theory, especially Quasispace.
Interstellar: Yes.  The Arilou have only one planet, their home.  This world
is hidden in a Quasispace pocket.  They can be found around the main
Hyperspace portal to Quasispace.  The Arilou craft is the Skiff, which is a
small single-entity craft that features excellent speed, apparent complete
inertial nulification, a weak autotracking laser cannon, no armor, and the
ability to teleport short distances.
Allies: No reciprocal alliances, but the Arilou consider Humanity their
wards.
Enemies: Many.  No race trusts the Arilou, and many will destroy them on
site.  The Orz hunt the Arilou, and the Arilou hate the Taalo for revealing
their secrets.
Comments:
 The history of the Ariloulaleelay is closely tied with the Androsynth, and
with the near-obliteration of that species much information has been lost.
What is known is that several hundred thousand years ago, the Androsynth
discovered a planet in Quasispace.  They found an odd Precursor device, once
which seemed to be designed to induce controlled evolution on a target at a
rate of millions of years a second.  This device was developed by the
Precursors as a means to undo their de-evolution.  With typical Androsynth
recklessness, they immediately experimented with the device, and ended up
creating several thousand Arilou.  (Ariloulaleelay is a corruption of the
Androsynth phrase for "thinking child").
 The Arilou quickly turned on their creators, driving them away from the
planet and using their enhanced telepathic abilities and Precursor
technology to wipe all knowledge of them from the Androsynth memory.  To
further drive the Androsynth away, they indoctrinated them with the belief
that they were clones of Humans from Earth, brought there by the Arilou.
The Androsynth had been studying them, the Jurai, and the primitive Syreen,
trying to figure out how such convergent evolution happened on close-by
planets.  The Arilou happily grew and prospered in their new home, taking
delight in generally being a nuisance in several nearby civilizations (the
Jurai particularly).
 It wasn't until relatively recent history (nearly two millenia ago) that
they discovered the tragic effects of their new home.  The very nature of
Quasispace was causing them slow genetic damage, and their continued use of
Androsynth breeding techniques (aka cloning) had merely caused the damage to
build up over the millenia.  They immediately turned to the current
Androsynth as a source of fresh genetic material, but discovered that they
could only delay the damage this way, not reverse it.  With the Syreen and
Jurai considering the Arilou enemies, they had no alternative but to try
Humanity for their experiments.
 Due to the primitive technology at the time, the people of Earth were at
the Arilou's mercy.  The arrival of members of other races in the 13th and
20th centuries caused the Arilou to become more circumspect, but they did
not cease their experiments until after Second Impact, when a quarantine was
placed on the world for 50 years.  The regime that rose after the events
following Second Impact were more than able to detect and prevent any
further Arilou intrusions.
 The Arilou are a dying race, and they know it.  They are also remarkably
deceptive, claiming they have Humanity's best interests at heart at one
point, and then admitting when forced that they merely need Humanity to save
themselves.  They also claim credit for Humanity's large amount of Gifted,
even though it has been shown that such proliferation existed for the entire
history of the race.  They are persona non grata in every sphere of
influence.

Power Name: Androsynth
Major Race: Androsynth.  There is no variation in the Androsynth genome.
All Androsynth are genetically identical (excepting necessary variations for
the two sexes) and enter the society as fully matured beings.  Androsynth
are tall, slender, bald individuals that are remarkably attractive to other
Humaniform races.  They have red skin, and all body hair is of a dark blue.
Minor Races: None.
Technological Specialization: None.  Androsynth research anything and
everything, and do it well.
Interstellar: Yes.  The Androsynth are refugees, and can be found anywhere
and everywhere.  The Androsynth Guardian is very rare.  It is a layered
cylinder of red and blue crystaline and metal alloys, which can collapse
into a sphere at the captain's command.  In cylinder form, the ship is slow
and clumsy, and can fire a barrage of plasma bubbles that appear to home in
on enemy craft in a haphazard fashion.  In sphere form, the ship is highly
agile and almost invulnerable - the ship can be used to ram enemies to
devestating effect.
Allies: Jurai, Humanity, Syreen, Ur-Quan (these races protect the Androsynth
refugees - see comments)
Enemies: Orz, Arilou
Comments:
 The Androsynth, much like the other major Humaniform races, has its origins
shrouded in mystery.  What is known about the Androsynth is that they have a
history of pursuing knowledge and esthetics to a degree other races consider
unhealthy.  Long before they achieved contact with a single race they had
already travelled far down the road of eugenics, becoming a race of clones.
They achieved spaceflight before all other Humaniform races, and discovered
Hyperspace travel.  Upon discovering the problems associated with that mode,
they abandoned it and started research on alternate methods.
 Luckily for the Androsynth, their brilliance did not lead them to a
discovery for many thousands of years.  They eventually discovered
Quasispace, and the lone planet (in the near region, anyway) that carried
the Precursor device they'd use to create the Arilou.
 Following their reprogramming by the Arilou, the Androsynth began a covert
study of Earth and Jurai, hoping to use that intelligence to destroy their
new hated enemies.  However, with typical Androsynth singlemindedness, the
Androsynth continued their study of extra-dimensional travel.  Since they
had been all conditioned to avoid further research towards Quasispace, they
went in the opposite direction, and began to explore Subspace.
 This research led to the doom of the Androsynth.  They opened a permanent
subspace gateway on their homeworld, and made contact with a highly
technological subspace species called the Orz.  The Orz invaded their world
and devored the grand majority of the Androsynth, and proceeded to hunt the
rest, on and off planet.
 From a population of roughly twenty billion, only a few hundred thousand
Androsynth remain.  They are constantly hunted by the Orz, who seek to
destroy them with a fervor that is not understood by any other race, except
maybe the Arilou, and they're not talking.  The Androsynth took refuge with
the people of Jurai, the Syreen, and Humanity.  It was thanks to their
contact with a Taalo ambassador on Earth that enabled them to discover their
true past, and made the Arilou their true enemies.
 Upon the Taalo's tales of the Androsynth to the Ur-Quan, the Ur-Quan
declared the Androsynth under their protection as well.  It is commonly
believed the Ur-Quan did this because of their particular sympathy for the
Androsynth due to their telepathic manipulation by the Arilou.
 Androsynth can be found all over Humaniform space, usually in
highly-defended facilities or planets.  They tend to gravitate towards
positions in research and artwork, both fields in which they excel.