Zerg

The Zerg, (also known as "The Swarm") are a terrifying and ruthless amalgamation of biologically advanced, arthropoidal aliens. Dedicated to the pursuit of genetic perfection, the zerg relentlessly hunt down and assimilate advanced species across the galaxy. Incorporating useful genetic code into their own, they exterminate any species that might corrupt the purity of the zerg genome.

History
The original Zerg species was discovered on the ash world Zerus close to the center of the Milky Way Galaxy, by a group of the mysterious and ancient Xel'Naga, led by Amon. Normally, the Xel'naga avoided interference with the species they create, instead allowing two of them bearing purity of form and essence respectively to come together naturally and perpetuate the infinite cycle of the Xel'naga. However, Amon and his supporters opposed the cycle and so defied this notion through directly uplifting the two species that would meet their criteria. The renegade Xel'Naga proceeded with their Grand Experiment of evolution, first bestowing Purity of Form to the Protoss, who would go on to worship the Xel'naga as gods. Seeking a species to be granted Purity of Essence, Amon and his supporters bought their massive Worldships high above the ash planet Zerus.

The fallen Xel'Naga were more successful with their second venture than they could have imagined. They advanced the evolution of the most insignificant life form on Zerus, a race of miniature worm-like insectoids known as the Zerg. Through Xel'Naga proto-genetic manipulations, the Zerg survived the torrential firestorms of their world and thrived. Although extremely small and possessing no ability to manipulate their physical surroundings, the Zerg adapted to survive. They developed the ability to burrow into the flesh of less vulnerable species indigenous to Zerus. Feeding off the nutrients contained within the spinal fluids of their hosts, the Zerg learned to parasitically merge with their host creatures. Once they become capable of controlling the metabolic and anatomical processes of their hosts, the Zerg used their new bodies to manipulate their surroundings.

Zerg chemistry began to mutate and adapt according to the volume of new genetic material being processed. However, as diverse as the range of host creatures became, there was always the undeviating drive to consume only the most evolutionarily advanced species encountered. The Zerg were innately selective as to which species they consumed, ensuring that at every stage of their development they were at the top of the proverbial food chain. Any race that the Zerg came across that were deemed unworthy of assimilation was eradicated to further purify the strains.

The Xel'Naga soon made an alarming discovery. The original races assimilated by the Zerg were hardly recognizable after only a few generations of their inception. Somehow the Zerg had developed the ability to supercharge and steer the latent evolutionary processes within their host creatures. The host creatures feel prey to the effect of gradual physical mutations that caused all the various strains to grow armor piercing spines, razor-sharp limbs, and ultra dense carapaces. Over a surprisingly short amount of time, the strains grew to resemble a terrifyingly ravenous and unified race. In order to keep the Zerg under control, Amon and his followers created the Overmind.

Overmind


"Awaken my child, and embrace the glory that is your birthright. Know that I am the Overmind; the eternal will of the Swarm, and that you have been created to serve me."

- The Overmind to a Cerebrate

The Overmind was a bodiless, brain-like entity of indeterminate age. Even though throughout most of the story it doesn't possess a physical form, its essence has been represented by a large eye. At one point in StarCraft, the Overmind takes form and manifests itself on the surface of Aiur, the Protoss homeworld. The Overmind possess the power of re-incarnation. As long as it or its cerebrates aren't struck down by dark templar energies, it can rebirth any of its subordinates making the Zerg virtually immortal.

The Overmind was created by the Xel'Naga, remembering all too well of their failure with the Protoss a result of pushing the sapience of the fledgling species too quickly. The Xel'Naga, attempting to waylay the potential hazards of differing egos, decided to follow a different path with the burgeoning Zerg. The Xel'Naga structured the collective sapience of the Zerg into a unified, amalgamated 'Overmind'. The Overmind coalesced into a semi-sapient being that represented the primary drives and instincts of all the Zerg strains. As time passed, the Overmind developed the rudiments of personality and advanced intellect.

The Overmind did not directly relay orders to its minions. As new species were added to the Swarm, it began to relay orders telepathically through cerebrates, giant versions of the larvae. These Cerebrates, despite having names and personalities of their own, were effectively extensions of the Overmind itself and were effectively immortal. In the event a Cerebrate is killed, the Overmind will simply produce a new body for it whilst holding onto its consciousness in the meantime. Direct orders from the Cerebrates were relayed through Overlords and Queens.

The Overmind began to think of its future. In order to continue finding new species, it must leave Zerus. Extending its senses into space, it became aware of enormous space-faring organisms. It lured them to Zerus with its psychic abilities, then assimilated them into the Swarm. Soon all the Zerg had the ability to survive in space. The Xel'Naga considered this a triumph. The Zerg had not only survived their weaknesses, they had retained the purity of their terrible overriding essence.

During this time, the Xel'naga became aware of Amon's treachery, confronting him and his followers in orbit above Zerus. As the Overmind grew stronger, its senses extended into space over Zerus and detected the Xel’Naga Worldships in orbit. Cutting off its psionic link to the Xel'naga, the Overmind effectively hid itself from their view.

As Amon intended, the Overmind sent its minions into space, attacking the unsuspecting Xel'Naga. Despite the ancient race's best efforts, it was overwhelmed as the Zerg crashed into the hulls of its ships. Within a few hours the Zerg laid waste to the Xel'Naga fleet. The greater whole of the Xel'Naga was consumed by the raging, genetic whirlwind of the Zerg. The Overmind absorbed thousands of sapient Xel’Naga into itself, gaining their knowledge and insights and causing it to grow much more powerful. It learned the secrets of the sacred khaydarin crystals, and began to incorporate the energies of these crystals into its own. Through the substantial amount of knowledge gained from the Xel'naga, the Overmind was able to increase the level of sapience in many of the higher zerg strains, while still keeping them fully under its control. Despite this overwhelming force, a small number of Protoss survived and were able to banish Amon and his followers to the Void. As the Swarm departed Zerus, some stayed behind, maintaining their individual freedoms from the Overmind's influence. These became known as the Primal Zerg, who gathered in packs of their own choosing and hunted one another to fuel their own unique evolutions.

The Overmind dissected the memories of the Xel'naga experiments with the Protoss. The Zerg left the lifeless, burning world of Zerus and laid waste to every planet they found along their path. As they progressed slowly through the trackless dark between the stars, the Zerg assimilated only the strongest of the races that they came across. As the swarm inched closer to the Protoss homeworld it continued to build steadily, ever-increasing in size and power. Its main urge was to assimilate the most powerful race in the galaxy, uniting purity of form and of essence, to create a totally "perfect" being.

The Zerg eventually came into conflict with the warring factions of Humans colonised throughout the Koprulu Sector. Despite Humankind possessing limited psionic potential, the Overmind saw fit to assimilate them into the Swarm, and so invaded numerous colonies, only to be followed and driven back by the Protoss. A human faction, the Sons of Korhal, stole the designs for a psionic emitter from the Terran Confederacy. These devices were made to be used as a means of bringing the Zerg under Human control. Using such emitters, the Sons of Korhal summoned the Zerg to the planet Tarsonis, capital of the Confederacy. The Swarm decimated the planet, killing millions of Humans and destroying the Confederacy, leaving a power vacuum for the Sons of Korhal to exploit as they forced all Human factions in the Koprulu Sector to unite under the Terran Dominion.

Retreating to their stronghold, the volcanic planet Char, the Zerg encountered the Dark Templar, a faction of Protoss outcasts who drew their power from the Void, who were capable of permanently killing Cerebrates and severing their broods from the Overmind's control, reducing the Zerg to mindless feral beasts. However, the loss of Cerebrate Zasz enabled the Overmind to peer into the mind of the Dark Templar known as Zeratul and discover the location of the Protoss homeworld, Aiur. With this information, the Overmind launched a full-scale invasion of Aiur and even manifested its physical form over an ancient Xel'naga temple.

Despite quarrelling and even in-fighting among the Protoss, they accepted the aid of the Dark Templar and Humans in defending Aiur. Through the sacrifice of Executor Tassadar, the Overmind is destroyed and the Zerg Swarm is shattered.

Queen of Blades
The Queen of Blades is the being created when the Zerg assimilated the Terran known as Sarah Kerrigan. In her Human life, Kerrigan already had incredible strength, speed, and psychic abilities. After being infested, these abilities were augmented exponentially by the Overmind.

The Overmind was greatly disturbed and aware that the Protoss had become a highly psionic race, able to bend and warp the very fabric of reality to their whims. It sought a way to counter the awesome might of the Protoss, but found no answers among the genetic strains it devoured.

On the verge of despair, the Overmind made an amazing discovery. One of its deep-space probes found a race that occupied a dozen worlds, right under the shadow of the Protoss. The new race, called Humanity, was mere generations away from developing into a formidable psionic power. But the Overmind also knew that Humanity was still in its infant stages, hardly capable of defending itself against the ravenous Zerg. Although a short-lived and seemingly frail species, the Overmind knew that Humanity would be the final determinant in its victory over the Protoss. If it could assimilate the psionic potential of Humanity, the Overmind would have the ability to combat the Protoss on its own terms. The Overmind began to unfold its master plan to enslave Humanity.

Even though the Zerg were able to infest many Terrans, most Terrans didn't have the correct genetic material to work with in order to create a being that could rival the Protoss. Only a small population of the Terrans are born with this needed psychic potential, such as the specially trained ghosts agents. Ghosts epitomized the height of Human evolution and physical conditioning. Ghosts channel their psionic energies to augment their natural physical strength and endurance. Thus, a typical ghost is tougher, stronger, and faster than even a well-trained but otherwise average Terran. Exceptional ghosts exist that can tear through walls, run at remarkable speeds, and leap tall obstacles. Perhaps one of the strongest ghosts was Sarah Kerrigan, with a registered Psi index of 8. Kerrigan proved to be the perfect tool for the Zerg's twisted experiments.

Following the overthrow of the Terran Confederacy, Kerrigan was eventually betrayed by her superior and left for dead for the Zerg. The Zerg captured and infested Kerrigan imprisoning her within a chrysalis as the Zerg Hyper-evolutionary virus began to re-structure her DNA. Kerrigan finally awoke from her chrysalis and was 'reborn' into the swarm under the title Queen of Blades. Kerrigan's psionic abilities developed rapidly after unlocking the psychic blocks that were surgically implanted in her as a human. One ability she developed was psionic storm. More importantly, she could now sense the presence of the Protoss Tassadar on the planet. She also has the shared ability of a cerebrate to command and direct an entire brood. After the death of the Overmind, she would eventually compete with the remaining Cerebrates for rule of the Swarm. Through her manipulations, Kerrigan used the Humans and Protoss to destroy her rivals on her behalf, winning the Brood War and cementing herself as the supreme leader of the Zerg. To ensure no Zerg would challenge her rule, Kerrigan purged the remaining Cerebrates and replaced them with the Broodmothers.

Resurgence
Years after the Brood War, Human scientists became aware of a Xel'naga artefact known as the Keystone, a monolithic object which could contain vast amounts of psionic energies. These scientists, the Moebius Foundation, realised the Keystone could potentially be used to revert the Queen of Blades back to Human form. Learning about the Keystone, Kerrigan launched a full-scale war against the Terran Dominion to find the Keystone. However, with the intervention of Raynor's Raiders, the Keystone is assembled from its scattered components and bought to Char. After a gruelling campaign against the Zerg, the Keystone is activated and the Queen of Blades is made Sarah Kerrigan again, complete with her original personality and little memory of her time as the Zerg's leader. Without their Queen, the Zerg broods turned on each other. However, Zeratul had learned about the fallen Xel'naga Amon, of a prophecy about his return and the end of all things. Zeratul also discovered that the Overmind was driven to assimilate the Protoss due to a mental directive Amon had imposed on it, and that it created the Queen of Blades not only to gain an advantage over the Protoss, but also in the hope she could free the Zerg from Amon's influence.

When the Terran Dominion abducted James Raynor and faked his execution, Kerrigan, enraged and obsessed with vengeance, returned to the Zerg and led them against the Dominion and Protoss alike to reunify the Swarm. During this time, Zeratul lead her to Zerus, where she was mutated into the Queen of Blades once more, albeit with her own personality intact rather than the influence of Amon or the Overmind. She later learned about Amon from the Primal Zerg and discovered that his ally, a Xel'naga known as Narud, had created an army of Zerg-Protoss hybrids for Amon. The Zerg eventually invaded Korhal in pursuit of Arcturus Mengsk, Emperor of the Dominion and Kerrigan's former commander before he betrayed and abandoned her to the Zerg on Tarsonis. However, Valyrian Mengsk successfully convinced her to direct the Zerg away from the civilian population. With the aid of Raynor's Raiders, Kerrigan executed Mengsk and departed to find and confront Amon.

The End War
Using the energy drawn from Kerrigan into the Keystone on Char, Narud was able to return Amon from the Void. Unleashing the Zerg-Protoss Hybrids, Amon was able to enthrall vast armies of Humans, Protoss and Zerg, using the Hybrids like commanding officers. Amon's Zerg were among his most prominent forces throughout the End War, although he was unable to control those Zerg under the direct control of Kerrigan and her Broodmothers. After the Protoss defeat Amon and drive him back to the Void, Kerrigan organises an alliance of Zerg, Protoss and Humans to venture into the Void and finish him off. To destroy Amon, Kerrigan is imbued with the essence of the Xel'naga Ouros and becomes a Xel'naga herself, destroying Amon shortly afterwards. Before departing the known universe, Kerrigan names Broodmother Zagara as her successor and provides the Swarm with a small amount of Xel'naga essence. Now Overqueen of the Swarm, Zagara used the essence to terraform many worlds left barren by the Zerg and now actively seeks peaceful co-existence between the Zerg, Protoss and Humans.

Genome
Zerg genetics is ever-changing. A group of cells, classed simply as "Cell group A"-presumably the Zerg Retrovirus-randomly mutates, and their immune systems (Cell group B) ruthlessly hunt down those mutant cells. If the mutant cells survive long enough, they become assimilated throughout the organism (threshold unknown). This invokes "Survival of the fittest" at a genetic level. Zerg evolve a million times more in a week than humans ever have. Zerg alpha amino acids have unique R-groups that allow damaged cells to assimilate free-floating proteins to repair themselves. This is what allows for their rapid healing factor.

Life Cycle
The swarm is separated into a number of broods which the terrans named after monstrous mythological creatures, predominantly from Norse mythology. As for the term 'Zerg' itself, it isn't known whether the terrans or the Protoss cointed the term since the Zerg has never referred to themselves as the Zerg or used the word in any way. The Primal Zerg have been known to refer to the Swarm as the "corrupted Zerg", a reference to Amon's tampering that divided the species between the Swarm and Primal Zerg. They only call themselves the Swarm. Each brood serves a specific purpose and is controlled by a Cerebrate that is genetically incapable of disobeying the Overmind.

The Zerg possess the ability to terraform any planet or space platform they land on through a thick mat of purple flesh called "Creep", which spreads out from Hatcheries, Lairs, Hives and Creep Colonies, the latter of which can be mutated into defense strains. Each structure in a Zerg Hive Cluster acts as an organ in a huge super-organism, some of which have spread out to cover entire planets or platforms.

Larvae
The Larvae is spawned from the Hatcheries, Lairs, and Hives. Each larvae carries the genetic code for every Zerg strain. At first, the larvae can only mutate into Drones and Overlords, although each new organic building adds more genetic information to their repertoire thanks to the hive mind and super-organism structuring of a Zerg Hive Cluster.

Egg
"Egg" is a misnomer: it is in fact a pupae. Larvae will enter this stage once they have received a command to mutate into one of the many strains of Zerg.

Adulthood
The mutated Larvae is now combat ready. Certain strains are for melee, ranged combat, or air support while others are solely meant to produce horrible poisons. Only the Hatchery/Lair/Hive and Queen carry out any reproduction. Very few Zerg have ever lived out their natural lifespans, as they are usually killed in battle. I is thought that they could potentially even be immortal thanks to their high rate of cellular regereration. The few exceptions are simply meant as distractions. If it is a ground based creature, it can burrow in to the ground.

Varieties
There are Numerous combative sub-species of Zerg.
 * Drone: responsible for collecting Crystal and Vespene, and construction.
 * Overlord: radiates Psychic energy to control the other Zerg with. It can be evolved into a transport class unit.
 * Zergling: evolved from small lizards, now the primary warrior strain. Spawned two at a time due to their simplistic genetic structure.
 * Hydralisk: large snake-like beast, derived from large centipede-like creatures, produces spines that are hurled with enough velocity to puncture battlecruiser grade armor.
 * Lurker: the lurker, using scythe-like arms and new found legs, mutated from the Hydralisk. It burrows and sends a row of vertical spikes into a target.(Brood war only)
 * Mutalisk: primary air combat unit. Each shot is a small flying organism which attacks three targets at a time.
 * Guardian: a crab like bomber creature mutated from a Mutalisk. Can only attack ground targets.(SC1 only)
 * Devourer: mutated from the Mutalisk. Can only attack air targets.(Brood war only)
 * Scourge: a small bat-like suicidal aerial unit, spawned two at a time due to their simplistic genetic structure.(SC1 only)
 * Queen (Pre Brood war): a large beast that originally resembled a sort of flying octopus, although they now move about along the ground for better protection at the cost of mobility. It is used to sow the hyper evolutionary virus, which in turn creates the Infested Terrans. Its only combat ability is spawning a pair of Broodlings on a ground unit.(SC1 only)
 * Broodling: a small, insectoid being that is fired from a Queen during its egg stage. It uses the targeted organism's DNA to fertilize it, and it is quickly born thereafter in an explosion of gore. They are vulnerable to any atmosphere, however, and cannot live for very long.
 * Defiler: a rove beetle-or scorpion shaped creature (specifically, a devil's coach horse beetle or a king scoprion). It carries the gene codes of every Zerg, which it uses to produce carcinogenic (cancer-causing) poisons.(SC1 only)
 * Ultralisks: a large Triceritops like beast. The term "Living Battering Ram" is most appropriate.
 * Infested Terrans (Pre Brood War): a "zombified" suicide bomber. It produces chemicals that are not only horribly toxic, but highly acidic as well.(SC1 only)

Post Brood War Strains

 * Nydus Worm: a long worm-like organism that erupts from the ground and drops off other units. It is actually a tentacle of the Nydus Network. presumably uses perstalsis to move Zerg combat organisms very quickly. it also grows Creep.
 * Infestor: a Zerg that resembles an armored slug that can put other Zerg in a frenzy, Mind control other creatures, Move while burrowed, spawn Infested Terrans: and spit a gob of fungal spores at enemy warriors.
 * Infested Terran (Post brood war): the evolution of Infested Terrans. They have a poisonous attack instead of its predecessor's destructive suicide attack. At the end of their short lifespan, the vesige of the original human's personality manages to exert just enough control over their new forms to kill themself. A different strain extends the period to a full planetary night, however, they spontaneously combust when exposed to UV radiation.
 * Neural Parasite: a small parasitic organism that is fired into an enemy soldier. It extends it's tentacles into the hosts brain, where it works their body like a marionnette.
 * Corrupter: a flying, vaguely spherical organism that can make it's victims weaker.
 * Overseer: an evolved Overlord with detection capabilities and has the power to disable buildings and spawn Changelings.
 * Roach: a ranged attacker with a supercharged regeneration ability and has the power to move while burrowed.
 * Brood lord: a Guardian like creature evolved from the corruptor that spawns Broodlings every time it attacks.
 * Queen (Post brood war): A new version of the queen, acts as a general/hive defender/overseer that can restore life, spawn extra larvae and creep tumors, pod-like organisms that produce creep. Once spawned, Creep Tumors may spawn one more Creep Tumor. This ability is passed on to its clone.
 * Baneling: mutated from the zergling. It is a small, suicidal, Pillbug-like kamikaze creature.
 * Changeling: a shape-chagging spy unit. It has a short lifespan.
 * Broodmother: An advanced form of Queen, Broodmothers replace the Cerebrates as the leaders of the Broods. They retain independent personalities, but are compelled to obey the Swarm's leaders. One Broodmother, Zagara, becomes the Queen of Blades' lieutenant and even successor after the End War.

Hive Mind
The Xel'Naga were concerned that the individuality of each Zerg would cause a war, and therefore they chose to impose a hive mind on their creation, which became known as the Overmind. Later, the Zerg were taken control of by the infested remains of the former human, Sarah Kerrigan, after the Overmind was obliterated.

Hierarchy

 * Overmind/ Queen of Blades/Overqueen
 * Cerebrate/ Brood Mother
 * Overlord
 * Queen
 * Minions