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Dennis was the first and most successful Project Tamed specimen. It participated in a demonstration, where Leow showed how the Tamed would obey her commands thanks to the implantation of a pathogenic prionic organism. His actions spooked the observers, and Loew was forced to pacify him. However, his act convinced the Dominion to give her funding, and as such, she rewarded Dennis with an extra slab of meat.
Weeks later, Dennis and the Tamed were deployed to Thys to eradicate feral zerg threatening terran colonists. Afterwards, they turned on the accompanying Dominion forces at Loew's orders, who was unwilling to use the Tamed to deal with the colonists (who were considered malcontents). With that done, Leow tried to activate somnus, to put Dennis and the creatures down. However, nothing happened—the Tamed had never been under Loew's control at all, and they proceeded to eradicate the remaining Dominion forces and colonists. As the Tamed slunk off, only Dennis remained. Dennis remained in place, and for a moment, Leow believed that he was still under her control. In fact, Dennis was under control of the Queen of Blades, and always had been. At the queen's direction, he gave Loew time to flee before killing her.