In StarCraft, the Zergs’ original homeworld is Zerus.
Zerus is presented in StarCraft lore as the planet where the Zerg evolved before the Xel'Naga altered their development. The planet’s harsh environment helped shape the Zerg into adaptable, predatory organisms capable of surviving through rapid biological change.
Players learn more about Zerus in StarCraft II: Heart of the Swarm, when Sarah Kerrigan returns there during her campaign. The planet is important because it contains the primal Zerg, an older form of Zerg life that developed without the Overmind’s control.
Zerus is sometimes confused with Char, another major Zerg-associated world. Char became a central Zerg base and battlefield, but it is not the species’ original homeworld. Aiur, meanwhile, is the Protoss homeworld.