Van Kleiss is referred to as a "mad scientist, only a lot more deadly" by Rex. He is ruler of his underground kingdom, Abyssus, and can control everything with in its territory (however, outside this terrain his powers are inaccessable).
As Rex attempts to split him in two with the BFS, it is shown thus far that it is seemingly impossible for him to die on his own turf (as his body immediatly regenerated). Unlike Rex, his body is less coopertive to the nanites, thus it is unstable and he must live off of a "constant supply of fresh nanites to survive". In the pilot episode, it is proven that he does this by extracting natites from captured EVO victims with his claw until they are robbed dry. The victims are left petrified in a rock-like formation and placed in his "garden".
Van Kleiss's golden bio-mechanical arm
It is also suggested that he had a hand in Rex's mutation, as well had a part in the Nanite accident five years previously, as he is bound to the same land in which the event took place, as well as mentioning that he and Rex were present at the time. He (along with Dr. Rylander) was assumed dead as of the episode Dark Passage.
Van Kleiss's Pack minnions include:
- Biowolf
- Skalamander
- Breach
- Circe (eventually defected)
- Nightshadow
- Bnok