Harrison Stacker, known by the nickname "Stacks," is a mechanically augmented patient at Facility 451. During the events of Deus Ex: Black Light, Stacks helps Adam Jensen escape from the facility, and accompanies Jensen in his return to Detroit.
In late 2028, Stacks meets Jensen after Jensen wakes up at Facility 451. When the other augs at the facility learn of Jensen's involvement at Panchaea, they turn on Jensen. Stacks helps Jensen fend off the crowd. The two later escape to Detroit, where they meet with Pritchard.
In early 2029, Stacks, Jensen, and Pritchard visit the Sarif Industries Headquarters. While inside, Stacks loses control upon seeing augmentation components and mechanical limbs illuminated by red light, which crated an appearance of blood. Jensen helps Stacks regain control as he confirms that the parts he was seeing were not severed mechanical limbs.
Later, the three discover that Motor City Bangers have been looting augmentations from the now-abandoned Sarif Manufacturing Plant at Milwaukee Junction. Stacks accompanies Jensen to the plant. Their plan is to destroy the plant to prevent further looting. When Stacks is mortally wounded by the Bangers, he confesses that during the Aug Incident, he lost control and killed his family, severing their limbs during his loss of control. Stacks tells Jensen to leave before triggering the detonator and destroying the plant in the process.
As a steeplejack, Stacks was outfitted with heavy-gauge mechanical arms designed for hauling him up the side of derricks and lifting girders. Stacks' mechanical arms also had an extra thumb on each hand.
Jensen observed that Stacks's augments resembled parts of a construction vehicle scaled down to human size and were strong enough to rip Jensen's cyberarms from their sockets.