Abathur

Abathur is a unique zerg creature. He is the zerg evolution master, serving as the Swarm's DNA library, and resides in the evolution chamber.

According to it, when a zerg strain's DNA evolves, it also becomes less flexible.

Biography
Abathur was created by the Overmind. After its death, Abathur became feral and purposeless. It wandered under Char, eating whatever tried to attack it.

It was discovered by Sarah Kerrigan and given a purpose.