Rephaim

The Rephaim were an invading species from outside the quadrant who attacked in the 24th century

Origins

The Rephaim were an unknown, invasive species whose true origins are unknown to the Terrans.
First encountered out on the Western edge of the frontier by Terran colonists, the Rephaim were totally alien and completely hostile to all sentient life that they encountered.
Many theories were developed on the possible origins of the Rephaim including the idea that they were a bio-weapon of a distant or long-dead species but no one has ever been able to determine them.

Name -the Rephaim

As the "Rephaim" did not communicate in any way, they were named by the Terran colonists who first encountered them, naming them after an ancient mythological giant from biblical times.
The Rephaim, having no written or spoken language, did not appear to have a name for themselves.

Biology

The Rephaim themselves are a parasitic, snake or worm-like creature measuring no more than a few inches long and possessing very sharp mandibles.  The Rephaim is incredibly versatile and hardy, able to interface with any living thing that possesses a nervous system.
The Rephaim are able to bite into the nerve stem of a host, which is generally done to a dead host but if done to a living host, would kill them instantly.  They are then able to control the host body and move them around as a host-body, though Rephaim operating "drones" in such a way are unable to speak or communicate and do not appear to have access to the host's memories or thoughts or perhaps simply have no use for them.
The Rephaim prefer cold temperatures and generate a mild "cold" aura, reducing the temperature around them by a few degrees.  Rephaim will generally prefer to live in very cold places and were known to drive asteroids or other large objects into planets in order to effect "impact winter" to reduce the planets temperature.

Reanimation

Due to the Rephaims ability to reanimate all dead tissue, they are able to repurpose their enemies losses into more troops for their own army, therefore gaining strength as their enemy loses strength.  The Rephaim themselves appeared to be able to reproduce very quickly to take advantage of additional host bodies.

Psionic Ability

Individual Rephaim appear to have a latent psionic ability and they were able to communicate instantly and over huge distances using this ability.  They did not, however, seem to have any ability or interest in using their psionic gifts to communicate or read the minds of their enemies.
It is speculated that the Rephaim simply did not understand anything that was "thought" by a potential host.

Castes

The Rephaim, when they exist in large numbers, produce multiple castes and are able to use a strange form of bio-engineering to fuse host bodies into new shapes or even attach multiple hosts into one larger host.

Drone

The most common Rephaim was a drone.  This was a basic Rephaim inhabiting a host-body.  The Rephaim would reduce the temperature of the host body, sometimes taking them to below freezing and would, through some osmosis, cause them to grow long, sharp talons, often crusted with ice.
The host-body would also produce a venom which was lethal to most living organisms.

Warrior

A warrior was a drone adapted for combat purposes.  Warriors would often have additional bone or ice plates grafted onto their body to give them increased resistance to attacks and then would also gain "bone-guns" which would see them able to discharge shards of envenomed bone from slots in their wrists or arms.
Corpse-Hulk A "corpse Hulk" was a rare, heavy combat form of Rephaim created by fusing many host bodies together and then using ice to give them a strong shell.  These huge creatures were the shock troops of the Rephaim force and able to shatter heavy armour and cause terror in their targets.

Super-Mind

The "Super-Mind" was a seldom seen Rephaim evolved up from the lower forms.  Super-Minds resembled larger drones and were often "piloted" by several Rephaim who had linked their psionic gifts to help coordinate the lower forms.
Super-Minds showed a greater than average agility but were otherwise much the same as the others with the same ice like shells and venomous claws.

Speculated Hive-Mind

Due to their psionic communications, it was speculated that the Rephaim operated under some sort of hive-mind, though no one was ever able to find a higher form than the so-called "Super-Minds".  It is not known if the hive-mind even existed or, if it did, whether it was the gestalt of all the psionic powers of the Rephaim together

Space-Travel

The Rephaim did not appear to build their own ships and their "armada" of thousands of ships bore the signs of at least nineteen different unknown alien designs.  These ships, it would seem were overrun, and taken over by the Rephaim to be used as "vessels" to move their hosts
The Rephaim were generally poor at space combat and preferred simplistic ramming tactics or using launched ice darts from their ships.  Their main strength was in their huge numbers.

First Contact

In 2324, the so-called "Lost Colonies", a number of worlds settled in Tranoan space back in the 22nd and 23rd century who had chosen independence over rejoining the post Federation Terran state, began to report losing contact with the outlying colony worlds.
The Tranoan government was wary of intervening in what could be considered a Terran affair.
The Lost Colonies organized, with some small Tranoan aid, an expedition to see what had happened to their outlying worlds and outposts in 2332.  This expedition was lost and the lost colonies lacked the resources to send another one but began to build up their defenses and call on the Terran worlds for aid.
In 2342, the Braer McQaid administration set up a select committee to investigate the ongoing crisis in the lost colonies.  Whilst Senator Shen Axxelson made recommendations that a scouting mission should be sent, this was not acted upon.
In 2347 the Lost Colonies reported another world lost to "unknown aggressors".  They began to speak about asking the Tranoans for aid.
In 2351, the Cameron Vassey administration agreed to take action to help the lost colonies.  In 2352, Task Force Lancelot was dispatched to the lost colonies, with permission from the Tranoan Empire to pass through their space

Task Force Lancelot

Task Force Lancelot, under Admiral Rebekah Valane and consisting of 110 ships and over 200,000 marines was deployed to the Lost Colonies in March of 2352.  At the former colony world of Trylon, they finally encountered a Rephaim fleet in orbit consisting of over 600 ships with another 1000 or more nearby.
Admiral Valane deployed the Task Force to test the Rephaim's capabilities after all attempts at communication failed.  A Marine landing force was repelled on the planet's surface with heavy losses.
Task Force Lancelot withdrew to Fort Tintagel, which was felt to be the most defencible of the lost colonies.  Plans to evacuate the millions of colonists were drawn up.
By the end of the year, over 70,000 marines and sailors had been killed in action against the Rephaim.

Operation Citadel

In 2353, Task Force Lancelot was reinforced with another 100,000 marines and began "Operation Citadel", a defensive operation designed to make Fort Tintagel impregnable whilst a possible evacuation was planned and, if needs be, executed.
The marines deployed over 100,000 marines to Fort Tintagel whilst the Fleet tried to slow the Rephaim advance into the system.
The Rephaim's assault on the system began in 2354 with two major fleet engagements but the Rephaim fleet was just too large to force back and Rephaim landings began that year.  The marines fought heroically alongside militia from the colonies to hold back the invasion.
By 2355, the Rephaim had taken 30% of the planet and inflicted around 75,000 losses.  More marines were deployed to the system, though by now the routes into the planet were very dangerous.
Admiral Etrigar assumed command over the Task Force in May of 2355.  The Marines, reinforced with another 50,000 troops, finally destroy the last infected areas and the planet is "clean" again.  A major naval battle is fought and the Federated States Navy regains orbital control of the system.

Tranoan Intervention

In 2358, the Tranoan Empire agreed to support the Terran Naval effort and a successful cordon was created thanks in large part to superior Tranoan naval firepower.  The Rephaim expended many ships attempting to break through into Tranoan space but were unsuccessful.
In 2359, the colony of Fort Tintagel was evacuated with around half of its population resettling into Tranoan space and the rest returning to the Federated States

Dhau Incursion

In 2361 the Rephaim began to assault the Dhau border and were able to make landings on three different worlds, overrunning two of them
The highly populated Dhau worlds proved to be a huge boon for the Rephaim who added tens of millions to their numbers.  The Dhau Empire appeared to be ill-suited to take on the Rephaim with their usual advantage of numbers and bravery no use against the mindless Rephaim who simply reanimated every slain enemy.
In 2363, the Galactic Council debated intervening on behalf of the Dhau but this was rejected, in large part due to Tazzyn pressure but also due to the Tranoan's reluctance to help the Dhau.  The Federated States lobbied on behalf of the Dhau for intevention but it was rejected and the Everett Stargher administration could not muster enough political support to intervene.

Dhau Stalemate and the "Population Bomb"

For the next twenty years there was an uneasy stalemate as the Rephaim expanded slowly into Dhau territory. The Dhau simply could not stop the invasion and more and more Dhau were lost to the invaders, with some estimates believed to exceed two billion Dhau lost to the Rephaim.
The Rephaim's slow advance was largely attributed to running low on transport ships and a Dhau policy of simply destroying any ships on infected worlds, essentially a scorched earth tactic.
However many military strategists across the quadrant believed it was just a matter of time before a major Dhau world fell to the Rephaim and the "population bomb" of the most numerous race in the quadrant being infected by the Rephaim unleased an unstoppable tide of Rephaim across the quadrant.

Lightning Point Outbreak

In 2389, a secret bio-weapons testing facility on the planet Lighting Point saw a containment breach and several Rephaim subjects, grown and kept in captivity, escaped and infested the lab.  A Marine Recon force was deployed to restore order and bring back any usable data.
Of the twelve recon marines deployed, only three survived along with one researcher brought out and the entire facility was destroyed by a close focus nuke.
There was no subsequent infection and a cover story was put out about a viral outbreak on the planet

Taur'lier Intervention and Apparent Extinction

In the year 2398, the Taur'lier made a rare appearance at the Galactic Council and offered to make "one final intervention" on behalf of the younger races.  They would destroy the Rephaim and save the quadrant from the potential explosion of the Dhau population bomb.
This was debated at length and the Dhau were invited to give their view.  In a rare show of candour, the Dhau admitted that they would not be able to defeat the Rephaim alone.
The Council agreed in November of 2398 to ask the Taur'lier to intervene.  The Taur'lier made it clear that if they did intervene, it would be their final act in the quadrant.  Whilst the full understanding of this wasn't known, it was agreed to ask the Taur'lier to end the Rephaim threat.
In January of 2399 the Taur'lier fleet launched massive attacks against the Rephaim, wiping their entire fleet out in a very one-sided series of battles.  The Taur'leir then attacked all infected worlds from orbit, destroying entire continents until they were satisficed that the worlds were no longer infected.
When the Taur'lier finished their attack, their fleet returned to their homeworlds and the Taur'lier began their enigmatic exit of the quadrant.
Whilst the Rephaim were apparently utterly wiped out, more than 2 billion Dhau died during these attacks, something the Taur'lier hadn't warned of and didn't seem to think was a huge problem.  This caused a massive loss of confidence in the Dhau Imperial leadership which saw the Dhau Empire slip into civil war.

Study of Rephaim DNA

In the 2360s the medical research corporation PINNACLE managed to acquire samples of Rephaim DNA which they later used, in part, to create their revolutionary APOLLO treatment which all but stopped the aging process in Terrans, as well as making them immune to nearly all diseases
However, the treatments needed to be topped up regularly and long term users began to show signs of massive DNA changes, becoming increasingly intolerant of all but the coldest temperatures and, by more than 40 years of use, needing to live in a refrigerated environment.
The use of the APOLLO treatment appeared to die out when PINNACLE was bought out by Proteus KP