

Eventually, the central hive mind of the Swarm, the Overmind, attained true sapience through this infestation method, and quickly rebelled against the Xel'Naga as well, apparently eradicating their former masters before setting off into the universe, driven by their genetic need to assimilate the most powerful organic species and annihilate the rest. The Zerg were a simple insect species that was altered by the Xel'Naga to have a 'purity of essence', an internal drive to constantly improve themselves, something the Xel'Naga also gave them the ability to do the Zerg would "infest" other life forms and absorb entire species into their "Swarm" altering and improving the Zerg as a whole by adapting themselves with the new species' genetic quirks.

The Zerg were created by the mysterious Xel'Naga race after their first creation, the Protoss, rebelled against them.
