They were feared and hated by all creatures who valued their own lives.
Millenia ago, a great race rose to explore space. They settled vast stretches of lifeless space, spreading their own life into every corner.
Time passed, and their planets were pulled ever closer to the core of the galaxy. Still they kept in contact with their home world.
In a blink, all contact was lost with the home planet. Those on the planet looked up in futile hope at the ships above, ordered to save them, destined to fail. In an instant, the ships were gone.
Then, so were the people.
Bodies stretched, unimaginable pain was blocked off by a confused brain. A whole planet couldn't be given the technology that had allowed their ships to pass through mere wormholes unharmed.
By the time the planet was released from the galactic core, everything on it was dead.
The great race was devastated. Without their traditional home and nutrition source, they were forced to adapt to giving birth in space, living with irregular amounts of radiation, and watching their home animals fall into inbreeding, disease and extinction. Their own bodies grew warped, one half completely unusable, and the other short and stunted.
They developed technology to cope with this. Everywhere they went, they built and invented more. Without a home planet to unify them, these people fell into wars between themselves, just as they had before the planet's unification. They developed super weapons capable of destroying an entire ship, an entire fleet, an entire planet, an entire star.
The first supernova released by them proved to be their undoing.
Despite their superbly advanced ship-magnetic fields, the intense wave of energy and radiation destroyed every shield within reach, disrupted local planets, mutated those on board and their future generations. They were weakened, so greatly weakened that they destroyed the technology and all knowledge of it. They unified their vast, densely-packed empire. They tried to settle down again.
And found that their colonies were failing.
No matter where they put one, even if on a "dead" planet, once they had terraformed it to even the first level, the colonists would begin to die. The scientists called it "gut rot" among the citizens. A citizen would first lose all of his or her fur, and the skin would turn a sickly pale pink with the veins standing out as bright blue. Then all they'd have to do is step outside and catch a cold, a parasite, a sneeze or cough. Then they would die.
Doctors performed autopsies carefully, wondering whether the disease would still be virulent. They needn't worry; it only thrived on live bodies. The problem was not the disease; as untold generations ago, these people would have considered it a children's sickness.
The problem was the lack of an immune system.
The entire species' immune systems were beginning to break down. Children were born with little to no antibodies. All infants had to be immediately isolated from any outside sources of bacteria, and any sickened colonists were quarantined, and shot dead when the public wasn't looking.
They had no way of examining any sort of life, if it would kill them.
The colonies died off, and the last survivors were those that had never set their ships down to explore, which were actually very few. These ships stayed in orbit, not wasting a single volt of power.
The supplies were running dangerously low, and the species quickly learned to survive on adrenaline when it could. But what could adrenaline run on, if not food?
Then, a lone scientist had a spark of inspiration.
The entire species had been forced, generations ago, to don their right-sided armor in order to support their bodies. Why not, he reasoned, engineer the species' entire bodies to survive on electricity alone?
And that's exactly what he did.
Every newborn of the species was outfitted with the new super suit, which would not only isolate them from outside contaminants, but also recycle every drop of water in their bodies and run them solely on electrical power. This generation learned to harvest energy from solar flares and magnetic fields, and even developed a powerful technology that would spare the planet itself, but kill off every spark of life upon it. Their people could once again colonize, and expand via cloning technology and genetic manipulation, ensuring they would never die out from inbreeding as their animals had.
Over time, they colonized the entirety of the solar systems around the galactic core, never leaving one uninhabited. Their culture developed too, into an intense dislike and disgust of any sort of life other than them. Bacteria was to be despised, because it could kill them all too easily. Any other intelligent life could never be allowed to develop, because it might start what they started so long ago, and spread toxic life to every corner of the galaxy.
Over time, this dislike turned to hatred. Their disgust turned to pride.
A second race developed space travel, far out on one of the stretches of stars.