Waylon Jones

Early Life
Waylon Jones was orphaned early in life, losing his single mother, his father having abandoned them before his birth. Waylon was born with a birth defect that made his skin extremely dry, leaving him in constant need of moisture. As a result of his strange appearance, he was bullied by the other children in the orphanage. This led to a young Waylon biting one of the bullies ears off.

Following the incident, Waylon was taken to a new home by a social worker. His standard of living improved. He no longer had to interact with other children who were always so cruel. The adults surrounding him were so nice and understanding. Little did he know, they were running experiments on the troubled child.

"What's Happening To Me?!"
The experiments caused the child to grow at a rapid pace. His teeth fell out, soon replaced by razor sharp ones akin to a predator. He went blind for a period of time, when he regained his sight, he could see in the dark. He had trouble breathing and needed to be put on oxygen for a time, when he recovered it was discovered he could breath underwater. His hair fell out and his dry skin became slimy and scaly. This went on for a few years, until one day Waylon broke.

He wanted to know why this was happening, what was happening. When the men and women in the white coats refused to answer, he rampaged. The electric shock collar they had been using to subdue him no longer worked. Waylon escaped using his tremendous strength and unrivaled aggression he later became known for.

Rumors
The next few years, the man lived hidden away in the sewers. Ashamed of what he'd become, not wanting to be seen by anyone. Though there were a few sightings of him, causing a urban legend to be born. The "Killer Croc" in the sewers.

Mutating Further
Realizing he was still mutating in his years in isolation, Waylon decided he'd have to find a cure himself. He became obsessive over it. Venturing out of his safe haven, Waylon began tracking down those doctors that had experimented on him. He got information from them and killed them. This pattern let to Batman connecting it and finding him.

As a result of his run-ins with Batman, Waylon has developed a strong hatred for him. Wanting nothing more than to see him dead. While he still is looking for a cure, Waylon started to commit more crimes. This included murder of innocent citizens. The mutation causing him to became more predatory and bloodthirsty.

Batman Death Waltz
Killer Croc started working as a heavy for Roman Sionis. The money was good and he had more access to the information that he needed. Croc was send to kill Selina Kyle for Sionis. He destroyed her apartment and chased her and Jason Todd through the streets before losing them.

Killer Croc was present at the Sionis Steel Mill when the Bat Family came to apprehend Black Mask. Croc confronted Robin, Batgirl and Nightwing at the front entrance. He fought them three-on-one, eventually overwhelming all three of them. But they were saved by Mister Freeze who send Croc tumbling back down into the sewers.