Alvin and Theodore were a pair of macaques kept as lab animals in the Splice O' Life laboratory that was located in the Clamp Center building. At one point, Billy Peltzer, who had gone up to the lab to get Gizmo out of there, released the two monkeys from their cage as a distraction as he sneaked towards the exit. Later, when the gremlins invaded the building, both Alvin and Theodore were released from their cage again, this time by the gremlins, along with the rest of the lab animals, whereupon they sacredly ran off for survival.