|Voiced by||Troy Baker|
Van Kleiss is the main villain of Generator Rex. He is described as "every mad scientist you ever saw, only a lot freakier and more dangerous." Like Rex, he can control his Nanites, but, as his mutation is unstable, he has to absorb Nanites from other EVOs to sustain himself. His victims are petrified in the process. He controls a group of powerful EVOs known as the Pack.
Van Kleiss is currently stationed in a cave in Eternal Vistas near the border to Endsville in The Suburbs, not far from Marceline. The Unstable Nano currently in development at DexLabs assumes the form of Van Kleiss.
- It's widely speculated and possible that Van Kleiss may in fact be Rex's long lost brother. They share many resemblances with each other. They have similar hair color, eye color, and similar control over nanites by taking in others. However, they differ in effect: Rex's powers cure EVO's while Van Kleiss's are needed to keep him alive and seemingly kill his victims.