Amon

"As I was your beginning, so shall I be your end."

- The Dark Voice

The Dark Voice is a Void entity. It is the leader of the hybrids. Its goals include the eradication of the terrans, protoss, and zerg.

Antiquity
When the xel'naga began uplifting the zerg, they created the Overmind to control and direct the hive mind. But the Overmind was not given free will. It was given an overriding directive to destroy the protoss. The Dark Voice had a hand in this.

While the Dark Voice ultimately planned to eliminate the zerg, it considered the hybrids to be proof of the zerg's success in its greater plan. It intended to enslave the zerg and use them and the hybrids to wipe out the terrans and protoss. Once the hybrids were dominant, it would dispose of the zerg and reshape all life in its own image.

The Countervailing Pawns
The Overmind was not blind to its plight. It foresaw the apocalyptic outcome if the Dark Voice, whom it called "the Fallen One", was victorious. The creation of Infested Kerrigan was the Overmind's attempt to free the zerg and prevent that future. The Dark Voice recognized the threat that Kerrigan posed.

After the Overmind died, its vision was passed to Zeratul through Tassadar. The prelate made sure to warn Jim Raynor of Kerrigan's importance and to ensure her survival. Zeratul wondered if the Dark Voice was a xel'naga.