The Zerg are a fictional race in the StarCraft universe. The Zerg are separated into a number of broods that are named after monstrous mythological beasts, almost always from Norse mythology. Each brood serves a specific purpose and is controlled by a Cerebrate that is physically incapable of disobeying the Overmind, who rules over the Zerg as the leader of the Swarm.
Gameplay as the Zerg is characterised by speedy construction of a large number of units to overwhelm the enemy through superior numbers. Zerg units are far cheaper and easier to produce than their Terran and Protoss counterparts, but are correspondingly weaker in terms of the damage they can deal or withstand.
The Zerg use entirely organic technology. Their weapons are part of the physical make-up of the various warrior strains, and mainly consist of physical and chemical attacks. Zerg buildings are also living organisms, and must be constructed on an organic membrane called the creep which surrounds Zerg colonies. Players must build special structures to speed the growth of the creep and thus expand their base.
Players may upgrade certain units by researching new 'mutations' which augment their skills or alter the units purpose. For example, a speedy light air unit can be mutated into a heavily-armed air unit, albeit with vastly reduced movement.
Tactically, the Zerg are designed to be slightly stronger when using ground-based attacks as opposed to airborne attacks. Players can use very large numbers of cheap, fast units such as the Zergling as cannon-fodder, whilst causing greater damage with ranged attacks.
All Zerg are directly subject to the will of the Overmind, because of the group mind of the Zerg. In fact, it is a biological impossibility for them to oppose its directives. Only Cerebrates and Kerrigan have sentience, and control individual armies (called Broods), using Overlords as lieutenants to directly control the warriors and workers. The lesser Zerg minions are wholly dependent upon the Cerebrates and the Overlords for order. Should a Cerebrate die, its brood may run amok; the animalistic natures of individual Zerg emerge. When an Overlord dies, a Zerg player loses control points and must create more Overlords to replace the loss. Without these control points, additional Zerg units cannot be built until existing units die or more Overlords are created. Even Zerg buildings are living organisms and aren't built but grown. They act as organs in the body of the Zerg Hive Cluster.
Though Zerg are incapable of disobeying their masters, their masters can change. When the Overmind died, the Cerebrates had freedom to do as they please. Though most of the Cerebrates themselves chose to remain loyal to Daggoth, Kerrigan did not and fought with the Cerebrates for control over the Zerg. However, the minions under each Cerebrate were completely loyal to it and followed all orders even to fight another Zerg.
Zerg broods are mostly named after Norse mythological monsters (Jormungand, Garm, Surtur, etc.). However, at least two broods have been named from another source. The Leviathan Brood was named after the Leviathan, a Hebrew mythological sea monster and the Grendel Brood was named after Grendel, the monster in the epic poem, Beowulf.
The history of the Zerg in the StarCraft universe began when the ancestral Zerg species was discovered on the irradiated, unstable planet of Zerus, by the ancient and mysterious Xel'Naga civilization, shortly after they had abandoned the Protoss on Aiur as a failure. The ancestral Zerg organisms were small and weak larva-like creatures, but they contained the purity of essence the Xel'Naga sought, being capable of surviving and thriving in a staggering variety of ecological conditions.
With the help of the Xel'Naga's gifts of proto-genetic manipulations, the Zerg survived the horrendous firestorms of their world and thrived. As the Xel'Naga pushed their development, they eventually began to develop the ability to burrow into the spinal columns of some stronger creatures on Zerus, parasitically merging with their nervous systems. These new bodies would then be used to manipulate their surroundings as the old bodies once did. The Zerg began to assimilate the genetic strains and processes of these host animals. However, as the Zerg had an undeviating drive to consume only the most advanced species they encountered, they eradicated lesser, weaker species. The Xel'Naga were surprised to find how quickly the Zerg could steer the evolution of their host creatures. Some of the things the Zerg developed in their hosts were armor-piercing spines, razor-sharp claws, corrosive saliva, and ultra-dense metallic carapaces within only a few generations of controlling new species.
Wary of the chaotic infighting that had enveloped the Protoss, the Xel'Naga created the Overmind, an enormous brain-like being, to bring order to the Zerg. At first it was only a semi-sapient entity created from the instincts and collective sentience of the Zerg, but it quickly evolved.
The Overmind did not directly communicate orders to its minions. As new species were added to the Swarm, it began to relay orders through Cerebrates, giant versions of the original Zerg insectoids acting as subordinates to it. Orders were relayed through Overlords, which were then given Queens to allow for the Zerg to operate in the most efficient manner possible.
The Overmind began to think of its future. In order to continue finding new species to assimilate, it needed to leave Zerus and travel to new worlds. Extending its senses into space, it discovered enormous space-faring organisms. It lured them to Zerus with its psychic abilities and assimilated them into the Swarm as the Zerus races had been. Soon all the Zerg had the ability to travel between worlds with reinforced carapaces to counter the vacuum of space. The Xel'Naga considered this a triumph. The Zerg had not only overcome their weaknesses, but had also retained their purity of essence.
The Overmind extended itself further into space, becoming aware of the Xel'Naga Worldships in orbit above Zerus. The Overmind then had its psionic link with the Xel'Naga severed — the Overmind effectively hid itself from their view.
The Overmind sent its minions into space, attacking the unsuspecting Xel'Naga. The helpless Xel'Naga tried to pull away from the planet. However, they were overwhelmed and the Zerg destroyed them. Within a few hours the Zerg had laid waste to the Xel'Naga fleet. Most of the Xel'Naga were consumed by the Zerg, and the Overmind gained their knowledge and insights. Processing thousands of sapient beings into itself caused the Overmind to grow much more powerful. It learned the secrets of the Khaydarin Crystals, and began to incorporate the energies of these crystals into itself. Through the 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, ironically helping to achieve the goal of the Xel'Naga.
The Overmind dissected the memories of the Xel'Naga experiments with the Protoss, learning of the failure, success, and the great benefit in assimilating such a powerful race. The Zerg then devoted their energies to seeking out the powerful Protoss in the hope of absorbing them into the Swarm, uniting purity of form and of essence to complete themselves.
As Episode I begins, The Zerg have infested Mar Sara and are killing the native Terrans. They conquer the planet, but the Protoss fleet under Executor Tassadar destroyed all life on it. Though the Zerg were used by the Confederacy to attack disloyal worlds, the Sons of Korhal turned it against them by using Psi Emitters to attack the Confederate capital world of Tarsonis. Despite, at one point, being protected by a group of Terrans against the Protoss fleet at New Gettysburg, the Zerg overwhelmed the defences of these Terrans and took Sarah Kerrigan hostage in the process. This ends the Zerg participation in Episode I.
In Episode II, a new Cerebrate is created by the Overmind to take control of a new brood. This young Cerebrate (the player) has at first only one task: To safeguard a Chrysalis. At first, the Cerebrate is tutored by the elder Cerebrates Daggoth and Zasz, who teach the Cerebrate the basics of the Zerg Hive Cluster. They inform and help the Cerebrate, giving stronger breeds to it, in its battles against the remaining Confederate and Protoss forces on Tarsonis before leaving the planet for Char.
On Char the Chrysalis becomes mature and sends out psychic calls to Terrans and Protoss alike. The Cerebrate is told to hold off the forces of the Terran Dominion and Raynor's Raiders. While battling Raynor's men, the Chrysalis hatches and Sarah Kerrigan is born into her new body. Kerrigan, under guidance from the Cerebrate and a couple of Daggoth's strongest Hunter Killers, enters a Science Vessel, hoping to find a way to gain access to more of her powers to further aid the Swarm. After gaining these powers, she instantly felt the presence of Protoss forces on Char, being led by Tassadar. Despite Zasz's disliking of going into battle against the Protoss, Kerrigan refuses to accept Zasz's warning and attacks Tassadar's base with the help of the Cerebrate and the Jormungand Brood. After the base is destroyed Tassadar agrees to battle Kerrigan alone, but ends up creating a mere illusion to fight her.
One hour later after Tassadar's disappearance, Daggoth informs Kerrigan that Zasz is dead. Daggoth orders the Cerebrate to cull the rampaging Garm Brood since they have begun to run amok with the death of their Cerebrate. Daggoth and Kerrigan at the time, began to set their trap to capture Zasz's assassin. After the culling of the Garm Brood, the Cerebrate swarms the Protoss base safeguarding Zasz's assassins after Daggoth and Kerrigan successfully established the blockade, and found out that Zeratul and his Dark Templar happen to be Zasz's killers. Zeratul and the Dark Templar were soon locked away in a Terran Installation, and the Overmind, who actually found out about the Protoss homeworld at the moment Zasz was murdered, ordered the invasion of Aiur. Kerrigan stood back in the invasion to safeguard the Hive Cluster holding Zeratul prisoner.
At this point, the young Cerebrate became one of the Overmind's commanding Cerebrates, and led the attack on the Protoss homeworld of Aiur with the Jormungand Brood. The Cerebrate swarmed through massive Protoss resistance, but eventually reached the Khaydarin Crystals. With a piece of the Crystal harvested, the Cerebrate then led another Brood swarm on the Protoss Temple. The Temple was destroyed and the Khaydarin crystal was put in its place. The location ends up being where the Overmind plants itself on Aiur. Afterwards, the invasion of Aiur continued and the Zerg slaughtering of the Protoss forces marks a horrific scene in Starcraft history. Soon after, Episode II ends.
In the final part of StarCraft, Episode III, the Zerg begin to lose ground. They are halted in their advance and have Tassadar and the Dark Templar escape their custody on Char. After this, two of their Cerebrates are killed and next, the Overmind itself. With the death of the Overmind, Episode III and StarCraft ends and goes on to StarCraft: Brood War.
The Zerg were originally controlled by the Overmind, who was destroyed by the Protoss, Tassadar (at the cost of his own life) at the end of StarCraft Episode III.
By Episode IV, the Zerg on Aiur had run amok after the death of the Overmind and having already slaughtered 70% of the Protoss, Zeratul led a number of Protoss survivors to the Protoss Warp Gate to escape to his homeworld of Shakuras to escape the Zerg. The Zerg, however, were able to follow Zeratul through the Warp Gate. On Shakuras the Zerg planted themselves around the Xel'Naga Temple before the Protoss arrived and liberated the Temple from the Zerg, even slaying its two Cerebrates.
After the deaths of the two Cerebrates, Kerrigan shows up and asks for assistance and to be allowed to reveal what she knows to the Matriarch. She revealed that the Zerg had formed a new Overmind on Char, the adopted Zerg homeworld. The Protoss, however, wanted something in return from Kerrigan before they decide to give Kerrigan support. Kerrigan assisted in retrieving two special crystals (Uraj and Khalis) that will activate the Xel'Naga Temple. On Braxis she assisted the Protoss herself and on Char, donating a Zerg Hive Cluster to the Protoss Fleet to provide back-up.
Back on Shakuras, a rebellion between the Protoss broke out so Kerrigan sat out of the fray until the very end where she assassinated Aldaris before he could get out valuable information about Kerrigan's plan. Zeratul banished Kerrigan and her minions from Shakuras due to this, saying that the rebellion was a pure Protoss matter. Kerrigan, however, was pleased with what the Protoss had done for her own cause, and despite being banished would come back to Shakuras, later on. The Zerg Broods then launched an all out attack on the Xel'Naga Temple and the remaining Protoss Forces, but failed due to the Protoss successfully activating the Temple, wiping out all Zerg life on Shakuras.
In Episode V, the Zerg don't appear as much as they did in Episode IV. At first, they appear on Tarsonis as four separate Zerg Broods protecting a powerful weapon known as the Psi Disrupter. The Hive Clusters are all wiped out by the UED Fleet when they located the structure.
The Zerg weren't seen again until the UED traveled to Aiur, where they waged a three-way-war between them, the two Zerg Broods and a Protoss base. The UED successfully destroyed the Protoss Base and the Zerg Hive Clusters, but were overrun by more Zerg reinforcements.
The Psi Disrupter, which was rebuilt on Braxis secretly, was infiltrated by Zerg thanks to Duran who had been hiding a secret that he is really an infested Zerg Hybrid. Duran, however, didn't fully succeed in destroying the Psi Disrupter in time due to the UED marines being able to stop the melt down of the structure in time.
With the Psi Disruptor working, the UED traveled to Char and attacked the Overmind, the UED had to battle some tough Zerg forces that included pumped up Sunken Colonies, Infested Terrans, and even the Torrasque. The UED, despite these opponents, prevailed and killed the Cerebrates that guarded the Overmind, causing the Zerg Broods to go amok and confused. The UED then succeeded in capturing the Overmind and turning its controlled swarms into the UED Renegade Swarm to destroy all opposition in the sector.
It is at this time that a Protoss Dark Templar discovers that Duran had been conducting experiments in combining zerg and protoss DNA using a combination of Human and Protoss technology. The resulting creature is discovered but is not destroyed.
In Episode VI, the final act to date, Sarah Kerrigan, a former Terran Ghost telepath soldier who had been infested (assimilated) by the Zerg, realized that the UED Fleet and their Renegade Swarm posed a great threat to her and her future plans so she took control of a Cerebrate (the player) of the Jormungand Brood and used his Broods to cleanse her Tarsonis Hive Cluster of the Renegade Swarms minions. Afterwards, she turned to bigger plans.
Kerrigan by this time had already had Jim Raynor, Fenix and their Protoss forces as allies (Duran acts as her second in command due to the fact that he is infested as well). She had sent Raynor to rescue Arcturus Mengsk in Korhal from the UED Fleet. Afterwards, Kerrigan, Raynor, Fenix, and Mengsk all agreed that the UED pose the biggest threat in the sector and agreed to ally with each other to fight the UED Fleet and their Overmind's swarm. Kerrigan first set her sight on the Psi Disruptor and after Raynor's Raiders successfully destroyed the structures generators, Mengsk dispatched an SCV with a Psi Emitter to gather the surrounding Zerg to Kerrigans cause. With the gathered Zerg from the Psi Emitter's call and the Zerg Broods from her Cerebrate, she attacked and completely destroyed the UED force dispatched to guard the Psi Disruptor and eventually destroyed the structure as well.
Mengsk wanted to retake Korhal as soon as possible, so Kerrigan traveled to the planet of Moria to pay the Kel-Morian-Combine a visit. The planet was rich with resources and was the perfect place to supply her forces. Fenix watched over the harvesting personally and surveyed over the amount of resources gathered. Kerrigan decided not only to take resources, but to also infest the Terran Command Centers to increase her forces. Once she was told they received enough resources, they set off to Korhal.
On Korhal, the battle was fierce, having to fight not only the UED establishments but also a Zerg Brood under their control. The Zerg Brood however didn't send many reinforcements, showing that the UED was having trouble controlling the Overmind at the time. Kerrigan, greatly supplied from the resources she gathered on Moria, and by the reinforcements of her infested Terrans, broke through the UED defenses and slaughtered all the UED soldiers and the Renegade Zerg, stationed in Korhal. After the battle, however, Kerrigan would do the unexpected.
Thanks to some knowledge gained from Duran, saying that the Protoss and Terran forces of her allies would be resting after the battle against the UED, Kerrigan launched a sneak attack on her unsuspecting allies of Fenix and Mengsk, quickly destroying their bases while they weren't able to ready themselves and eventually killing Fenix and General Edmund Duke. After the slaughtering, Mengsk and Raynor bitterly vowed revenge on Kerrigan for her treachery.
Kerrigan returned to Tarsonis to regroup and rest after the battle, as well as plan her next attack. Duran informed Kerrigan that the UED sent the Renegade Swarms to attack her Hive Cluster on Tarsonis, wiping out all her Hive Cluster's outposts. Kerrigan, with the help of her Cerebrate, launched a counter-attack against the Renegade Swarm and eventually destroyed the UED base in charge of the swarm's offensive. With the danger out of the way, Kerrigan decides it was time to return to Shakuras.
The attack on the Dark Templar wasn't easy due to the fact that Kerrigan was unable to use her airforces to reinforce her broods due to a protective shield in the area. Duran led the attack personally on the capital city of the Dark Templar and with his knowledge of Protoss technology overloaded the Pylon Clusters to explode and destroy most of the city. With the major distraction, Kerrigan was able to get into the city and take the Matriarch captive. She, along with her Brood, departed for Char.
Traveling to Char, Kerrigan was contacted by Zeratul, saying to release the Matriarch. Kerrigan, however, took the Matriarch, in order to force Zeratul to do something for her first before allowing the Matriarch to return to them. Zeratul was forced to accept and gave her some of his dark templar warriors as she and her Cerebrates Brood attacked the UED's Overmind directly. Fighting through large UED resistances and Renegade Broods, Kerrigan broke through the defenses and used the dark templar to destroy the Overmind. As it was beginning to hatch again, Zeratul came in and finished off the Overmind for good.
Afterwards, Kerrigan and the Matriarch came in and Zeratul, holding up his part of the bargain, demanded the return of the Matriarch. Kerrigan allowed her to go with him but the Matriarch decided that Kerrigan was her Mistress and she wanted to stay with Kerrigan. Zeratul, maddened by this, grabbed the Matriarch and was then 'Recalled' to a protoss base on Char, hoping to escape to Shakuras. In the hopes to get her back, Kerrigan launched an all-out offensive on Zeratul's base and was able to the destroy the base in time before Zeratul had the chance to be recalled to Shakuras. Zeratul at this point decided to kill his Matriarch rather than see her as Kerrigan's slave. The Matriarch thanked Zeratul in her final moments and anointed Zeratul the new leader of the Dark Templar before dying. Kerrigan, shocked at this sighting, allowed Zeratul to leave freely, saying she will be happy to see Zeratul live the rest of his life in grief and remorse rather than instant death.
Kerrigan traveled to the orbital platform overlooking Char to rest and regain her strength. Soon after, she is brought to the attention of three fleets approaching her position. The fleets consisted of Mengsk and the remnants of his Terran Dominion, Artanis and his Protoss forces, and Dugall and the remainders of his UED Fleet. Kerrigan's only defense she had was from her Cerebrate and his Jormungand Brood. Duran at this time had vanished, to the dismay of Kerrigan. A huge 3 on 1 battle between the Cerebrate's Brood and the three fleets took place on the orbital platform but each of the fleets eventually fell to the Cerebrate's Brood due to the lack of man-power and depleted resources. After the battle, Kerrigan took her place as the Zerg's 'Queen of Blades'.
With the Terran Dominion in ruins, the expeditionary fleet of the UED destroyed, the greater whole of the Protoss home world Aiur conquered by the Zerg with the survivors living on Shakuras, the Zerg currently stand as the dominant force of the Koprulu Sector.