Overmind

The Overmind was the first ruler of the zerg swarm and the first of its breed.

When the Xel'Naga arrived to Zerus, they discovered the original zerg insectoids. They spurred their evolution through proto-genetic manipulation. As time passed, they began mutating hosts into new breeds, and came together as a unified species. However, they were still individuals, and the Xel'Naga did not want a repeat of the protoss rebellion. To take away the zerg's individuality, the Xel'Naga created the first Overmind. The Overmind started as a semi-sentient being, but its intelligence and self-awareness secretly grew over the centuries. To begin the swarm's evolution, the Overmind created the first cerebrate, naming it Daggoth. He instructed Daggoth to begin hunting down new species for assimilation, and Daggoth followed. He was also told to treat his minions with care, as each loss reverberated in the core of Daggoth's own being. After centuries, the swarm dominated Zerus, and the Overmind discovered the location of the Xel'Naga fleet. He sent his many broods to destroy the fleet, at the cost of billions of zerg. To harvest minerals at better efficiency, the Overmind took Nargil's brood to Eldersthine, to find new species for assimilation. To easily assimilate the Gashyrr wasps, the Overmind created a geneticist to study and integrate new sequences. The wasps were assimilated, and the new drone caste was created. By that time, the construction of the Witness deep space array was complete, and it had discovered a new world, which would be home to a new species.

At one point, the swarm left Zerus and traveled to the Koprulu Sector, upon discovering the terran race. During this time, the protoss began to show themselves, and immediately tried to exterminate the zerg infestation, starting with the Confederate planet of Chau Sara. The Overmind found that the zerg could not assimilate the protoss, which the Xel'Naga had originally intended for the zerg to do. The zerg swarm based itself on Char, where they secretly grew in number. The Overmind supervised the kidnapping of Sarah Kerrigan and the destruction of the Confederacy. The Overmind instructed a cerebrate to guard Kerrigan's chrysalis while Abathur altered her sequences.

The Overmind had the ability to regenerate a cerebrate's exoskeleton had it been destroyed. However, he allowed for Zeratul to kill cerebrate Zasz, and managed to discover the location of Aiur. He led the invasion of Aiur before the Conclave could be warned, and a majority of the protoss race was then wiped out. The Overmind unwittingly embedded himself on Aiur, claiming that it would be the new zerg base of operations. Executor Tassadar fused his psionic energy with Void energy, and crashed his ship into the Overmind. The Void energy was the only thing that could truly kill the Overmind's consciousness, and the zerg on Aiur later became feral. The cerebrates, being unable to sustain themselves without the Overmind, would later die out or disappear completely.

During the Second Great War, Zeratul returned to the ruins of Aiur to find remnants of a vision the Overmind had centuries ago. He was greeted by Tassadar's spirit, who showed Zeratul a vision of an apocalyptic future where Kerrigan had died and could not stop Amon. Zeratul showed this vision to Jim Raynor, to convince him to save Kerrigan instead of kill her.

Zurvan had witnessed the Overmind's creation himself before falling into a deep sleep for millennia. When Kerrigan awakened him, Zurvan explained that the zerg's hive mind was considered corruption to the primal zerg.

In a possible future for the Swarm, Zagara had died and left Phyrexios in charge of the swarm. Phyrexios believed that his role was ending because no more information could be gathered, and he later died. However, he instructed broodmother Sakura to watch over Imperus' egg. When Imperus hatched, he could not recreate the leviathan strain. However, he contained essence from the Overmind and Abathur, so he could create a new space faring strain, the Terra Zerg. The Overmind and Abathur were able to communicate to Sakura through Imperus.