Ulrezaj's Slave Brood were zerg minions used by the Dark Templar terrorist Ulrezaj in an effort to clear the Dark Templar homeworld of Shakuras of the Khalai refugees which sheltered there after the Fall of Aiur. They would have been enhanced with Dark Templar energy.
Ulrezaj, imprisoned on Shakuras after murdering a number of Templar, escaped due to the actions of the terran mercenary force, Schezar's Scavengers. He stole a khaydarin crystal and fled to the world of Korhal. Zeratul and a protoss force followed him there, where they discovered zerg forces, acting in concert with the Scavengers. A khaydarin crystal was being used to control these zerg. The protoss forces chose to recover the crystal.
The protoss discovered that the khaydarin crystal was, in fact, warped. They were able to track another five warped crystals to Char, where Ulrezaj's forces sheltered along with five enslaved zerg broods which the crystals were controlling. Zeratul dispatched a small force of protoss warriors, including a Dark Archon Hero, to destroy the crystals. Doing so freed the zerg from the crystal's control, sending them into a state of dormancy.