In the original StarCraft, the Zerg hive mind's central leader is called the Overmind.
The Overmind directs the Zerg Swarm through its cerebrates, which function as powerful subordinate commanders. It sends the Zerg to invade human colonies and later targets the Protoss homeworld of Aiur. The Overmind is therefore the highest-ranking Zerg intelligence in the first game's main story.
The Overmind is often confused with Sarah Kerrigan, who becomes the Queen of Blades after the Zerg transform her. Kerrigan is a major Zerg leader, but she is not the original hive mind's central controller. Players may also confuse the Overmind with a cerebrate, the individual Zerg commanders who administer parts of the Swarm.
The original StarCraft campaign eventually reveals that the Overmind's plans involve controlling the Zerg against the Protoss. Its role establishes the faction's collective, hierarchical nature and sets up the central conflict of the game.