507

Like Ricky, 507 was created on the Albata Research Base under the Ares Project, but in an alternate timeline simply referred to as the Mirrorverse.

In the primary timeline, Karl saves Ricky simply to save him, as he sees all of the experimental subjects as people and values their lives. Ricky's body's failure to respond to the mutagen shouldn't deem him a failure, as he has strengths elsewhere, and ultimately moves on to do great things in the future because of this (with Karl's unwavering love and support of course).


In the Mirrorverse, Dr. Cattacopper sees Experiment 507 as a failure, a potential waste of time and resources, and a possible insult to his scientific genius. But he notes that the experimental subject shows promising intellect, so rather than having him put down, he takes ownership of 507 and "fixes" his defect via a full spinal transfusion of nanites, a completely experimental procedure.
The nanites work as a substitute for the failed mutagen (increasing his physical strength and sharpening his senses), as well as granting minor regenerative abilities. His spinal column can be accessed and the nanites can be altered through the ports in his back for further testing.

However, the nanite infusion procedure causes some neurological damage, resulting in increased obsessive-compulsive behavioral and personality patterns.
His head is always shaved for ease-of-access EEG testing.

His personality develops almost sociopathically due to Dr. Cattacopper's repeated abuse and manipulation.
Along with that, he is unable to differentiate his negative treatment from being "loved" by the geneticist who "saved" him, ultimately taking pride in being Dr. Cattacoppers "favorite" experimental subject, so much so that the very idea of anyone else encroaching on this territory disgusts and infuriates him.

By the time 507's obsession becomes apparent to Dr. Cattacopper, it's too late.

When a tear between the timelines allows the Ouroboros Division from the Primary to enter the Mirrorverse. Cattacopper is killed, and 507 subsequently kills the remaining members of the Mirrorverse division before leaving his own timeline through a tear in Limbo, ultimately arriving in the Primary with the intention of killing the remaining members of the Ouroboros Division.

His trip through Limbo was not without a toll: despite surviving the ambient radiation due to his nanites, 507 picks up a hitch hiking entity that enters his thoughts, insisting that it can help him if he helps it... and that it can even bring back his lost scientist.