The Undermind: The Eternal Fury of The Swarm
It all began on Zerus. After The Overmind assimilated the Xel'Naga, and before they departed their homeworld, The Overmind collected the primal essences from every Essence Pool, even the First Spawning Pool, and packed all of those essences within a Chrysalis. The Overmind believed that, after 1000 years of growth and evolution, the chrysalis would hatch, unleashing a Supreme Being that would benefit the Swarm in battle. As the Zerg consumed more and more species in their interstellar rampage, The Overmind added these genomes to the Chrysalis. Rather than assign a Cerebrate to watch over it's prize, The Overmind decided that it would watch over the Chrysalis itself. The Chrysalis continued to grow, and it finally hatched during a conflict known as the Swarm War (the basic rundown: 3 Xel'Naga survived the Overmind's attack, and decided to make a second Overmind with it's own swarm, giving it a primary directive to destroy the Zerg and peacefully merge with the Protoss, rather than assimilate.) The Undermind helped the Zerg destroy the False Overmind of the Xel'Naga Swarm, thus assimilating the second swarm into the original one. The Undermind was given 3 primary directives: to evolve the Swarm, to ensure the Survival of the Zerg species, and to assimilate the Protoss.
The Undermind had the ability to instantly morph into and Zerg unit or structure, like a changeling. It's preffered form was that of a Defiler, and it was The Undermind who invented the Defiler strain in the first place. At first, The Undermind resided within the depths of the Tiamat Brood, but it soon created it's own Brood. The Plague Brood had 2 primary directives: to evolve the Swarm and to produce more warriors. It would harvest as many resources as possible, spend all of them on units and upgrades, and then it would distribute the produced warriors evenly to all the other broods. Because it was made to provide reinforcement, the Plague Brood was more of an Industrial Brood than a Combat one. The Undermind constantly worked to further evolve the defiler strain, believing it's bio-plagues to be the most powerful weapon in the Swarm's arsenal. Though it was not like the other Cerebrates, The Undermind had the same power and intelligence of the Cerebrates, probably even more. The Overmind described the Undermind's strain as a Metamorph, a unique Zerg that could guide it's own evolution. When the Zerg arrived in the Koprulu Sector, The Undermind led the zerg invasion of Tarsones, and personally slaughtered the Confederate Council. The Undermind then continued to serve it's part in the Swarm, and was even re-born with the energies of the mythical Argus Stone. (see Starcraft: Retribution) The Undermind was the Cerebrate you play as for the last 2 missions of the Zerg Campaign, because the Cerebrate you played as in the rest of the campaign is with Kerrigan on Char during the Fall of Aiur. The Undermind then oversaw the manifestation of the Overmind, and then set out to assimilate the protoss. The Overmind was made manifest so that it could digest the biomass of the Protoss that fell on Aiur. This would make the Assimilation process easier. Though the Undermind did what it could to defend it's Master, Tassadar succeeded in destroying the Overmind. The Undermind was lost without it's father, and thus sided with Daggoth and the other Cerebrates, which Kerrigan called renegades for some reason. (she is the renegade who rebelled against the Cerebrates, not the other way around.) The Undermind believed that if Kerrigan succeeded to control the Zerg, then the Swarm would be doomed to extinction (he thought little of Kerrigan, believing her a "Stupid, filthy Human.") Unfortunately for The Undermind, his efforts were in vain. The UED invaded, and The Undermind's brethren were defeated. The Undermind himself is actually the last Cerebrate defending the New Overmind from the UED in the mission "to chain the beast." The Undermind then thought of a cunning plan. It disguised itself as just another Cerebrate, and pretended to be Kerrigan's pawn. The Cerebrate you play as in the Zerg campaign of the Brood War is The Undermind. During the interbellum, the four years of silence from the Zerg, Kerrigan ordered the extermination of the remaining Cerebrates under her command, but soon realized that they, and their Broods, had vanished without a sound. She was then contacted by The Undermind, but was unnable to locate the origin of the signal. The following is the conversation they had. This conversation is shown in the Zerg briefing room from SC1, and The Undermind is portrayed with a Defiler portrait.
Undermind: Hello, Kerrigan.
Kerrigan: What? who are you?
Undermind: I go by many names, little girl. You may best know me as the Cerebrate who "served" you during the Brood War. By the way, I will give you some credit. Your cunning was greater than what I thought you humans were capable of. But, I have been dying to tell you that your efforts to rule the swarm are futile.
Kerrigan: I see. And how do you expect to stay alive without an Overmind?
Undermind: You humans are so simple-minded and predictable. The Zerg adapt, The Zerg thrive. Like I said, your efforts are futile. One day you will be what you were born to be. The Overmind's little %^-*!.
Kerrigan: And what is to stop me from finding you?
Undermind: I have taken the majority of the Swarm from you. Even if you find us, you would be easily overcome by us. You don't seem to understand the situation your in right now. We will not be stopped. Not by you, or the Terrans, or the Protoss or anyone! We will revive the Overmind, and we will complete the Grand Experiment by assimilating the Protoss. You may search every nook and corner of the Koprulu Sector for even the slightest glimmer of our presence, it will do you no good. For I have seeded the Swarm on many, many worlds. You will not find a single one before we are ready. And when we are, we shall reap what we have sown......revenge.
*End of Briefing*
Since then, The Undermind has renamed his Plague Brood the Zerus Brood, and has named his Swarm the Primal Swarm. His Cerebrate brethren all pledge allegiance to him, and they are helping him consume and plunder new worlds in preparation for their return. Their swarm was in fact viewed on Aiur and on Haven. The Zerg than infested Haven's colonies were commanded by a Cerebrate, and all the Zerg on aiur are commanded by a large group of Overlords, which keep a constant psychic link with the Undermind himself. The Undermind has a spy among Kerrigan's Swarm: Abathur. The Undermind himself was the Giant Queen you fight in the WOL mission "Belly of the Beast", spawning an army to seemingly support Kerrigan, but to later overthrow her. However, his plans were foiled and he was temporarily slain by Jim Raynor. during and after the events of HOTS, the Underminds swarm is about 3 times larger than kerrigan's, and by far is more efficient and effective in combat. It is only a matter of time before the Primal Swarm returns to the Koprulu Sector. And because of the damage Kerrigan has done during HOTS. Korhal is vulnerable to attack, and would be a prime target.