Zerus

Zerus was the homeworld of the Zerg, and is an inhospitable planet that was wrought with severely unstable volcanic activity that was home to several species of giant insectoid creatures that were capable of surviving the harsh atmosphere.

History
The Xel'Naga &mdash; an advanced cosmic race that set to create and care for lesser races &mdash; journeyed through the universe to create a race with a purity of essence. The Xel'Naga settled on an ash-world named Zerus, and chose the most insignificant lifeform upon the planet: a larval creature known as the Zerg.

They nurtured these creatures, allowing them to affect their surroundings in almost parasitic ways. Eventually, they began infesting the creatures of the planet by burrowing themselves into the spinal cord of the creature and assimilating their DNA, turning them into monstrosities. The Zerg spread rapidly across the planet, infesting every living lifeform on the surface while rapidly growing in numbers.

It wasn't until the Zerg broke away from the control of the Xel'Naga and formed a hive mind that the Xel'Naga realized their mistake. Once the Zerg Overmind noticed that the Xel'Naga were always watching the Zerg, the Overmind hid deep within the planet in order to be undetected by these. It then launched an attack against them and Zerus became the site of the ultimate defeat of the Xel'Naga race.

The Zerg eventually abandoned the planet, leaving it a burning hunk of lifeless rock.