Van Kleiss

Van Kleiss is The recurring antagonist of the series. He is able to control his nanites like Rex, except his mutation is unstable and requires a constant supply of fresh nanites, causing his victims to petrify in the process. With the Pack as his enforcers, he established a domain called Abysus at the original site of the nanite explosion and has nanites seeded for miles in the area. As a result, he can control everything in his sphere of influence, and even regenerate completely from the ground if his body is destroyed. He has an extensive knowledge about the nanites, apparently having worked on or been familiar with the experiment which released them, and about Rex's past. He is killed in Dark Passage while attempting to secure Dr. Gabriel Rylander's nanite laboratory, but was resurrected in What Lies Beneath when Rex had to resurrect him with a machine when Abysus was becoming unstable. Rex cured him shortly thereafter. In doing so however, Rex gave Van Kleiss the means to study his nanites, which Van Kleiss then stole. With Rex's nanites, Van Kleiss gained the new power to create E.V.O.s simply by touching his victim, which passes them a unique mark. It is said that E.V.O.s created by Van Kleiss have their nanites extremely unstable, meaning that the transformation will eventually be permanent if not cured.

The Pack

 * Biowulf (voiced by Troy Baker) - A blue-armored, white-haired, werewolf-like E.V.O. with superhuman abilities that is fiercely loyal to Van Kleiss. Due to Van Kleiss' powers being limited to his native soil, Biowulf acts as the Pack's de-facto leader in the field. He was captured in Payback, but busted out in between Season 1 and Season 2, presumably by Breach.
 * Skalamander (voiced by John DiMaggio) - A large humanoid lizard-like E.V.O. with crystal spikes growing out of his body, four short stubby legs and a crystal club growing out of his left arm. His head also appears to be permanently twisted to its side. He can fire spikes out of the club or grow it into a shield. In Payback, Skalamander took part in Van Kleiss' attack on Providence. He had Dr. Holiday cornered until she unleashed her sister on him. He was presumably captured and later busted out by Breach.
 * Breach (voiced by Hynden Walch) - A disturbed black-haired female E.V.O. with four arms where the higher pair has oversized forearms. She has the ability to create portals of varying shapes and sizes for multiple purposes. Of all the Pack members, she speaks the least and acts on her own whims. She also uses a pocket dimension to hold a city she stole, which she uses to store her "toys" (referring to anything she liked, i.e., art, stolen property, E.V.O., etc.). Breach is obsessed with everything in this dimension being "neat", it being the only way she to maintain her sanity. In Breach, she attempted to trap Rex, but this backfired when Rex went on a rampage after learning of her obsession with cleanliness. In doing so, he drove Breach mad, causing her to collapse in on herself, allowing him to escape in the chaos. She eventually recovered returning in What Lies Beneath to rescue Van Kleiss at the last minute. Breach later took part in Van Kleiss' attack on Providence Base where she planted bombs throughout the base. Though Rex managed to disarm the bombs, Breach got away. Breach later stole a reactor core bound for Providence while Van Kleiss was fighting Rex.
 * Circe (voiced by Tara Sands) - Introduced in Beyond the Sea during Rex's trip to Cabo Luna, Circe is a female E.V.O. with black and red hair whose powers only manifest when active like Rex's. When activated, her mouth prolapses into a tube which she can use to project destructive sonic pulses, which also attract some other E.V.O.s to her. She is also skilled in kung fu. She tells Rex she has joined up with the Pack because she feels like too much of an outsider anywhere else, though Rex constantly tries to get her to switch sides. Van Kleiss acknowledges her friendship with Rex and allows her to join the Pack even though Rex had helped her in her initiation of defeating a sea monster E.V.O. He implies that he intends to use her to get to Rex. Rex has feelings for her, and she seems to reciprocate them, as evidenced by when they almost share a kiss, although Rex puts defeating Van Kleiss first over their relationship. Despite that Circe was almost left for dead by Van Kleiss when he bargained Rex to join the Pack or let his closest friends die in What Lies Beneath, Circe still remains with the Pack. After the events in Alliance, Circe strikes out on her own after Van Kleiss forbids her from helping Rex against NoFace.