Zerus

Zerus is an inhospitable planet wrought with severely unstable volcanic activity situated within the central regions of the Milky Way. It was the original home of the zerg and several species of resilient giant insectoid creatures.

History
Following the perceived failure of the protoss, the xel'naga set off once more to create the perfect lifeform. They discovered Zerus and the zerg, the most insignificant lifeform upon the planet. Using the zerg as the base the xel'naga continued their grand experiment. The development of the zerg reached its climax when the nascent Overmind broke away from the xel'naga's control and launched an attack on its progenitors. Having absorbed a portion of the xel'naga's knowledge, the zerg ascended to the stars to seek their destiny and the protoss. Zerus was left a lifeless rock.