Hallocat (previously known as 'Pookey' before the mutation) was a truckers pet cat, his owner had been illegally dumping toxic waste for a chemical plant whose foreman did not want to dispose of the waste properly in an effort to cut costs. One day, Pookey got under the foreman's feet, tripping him. In a fit of anger, the foreman picked him up and threw him into a vat of toxic waste (which was actually mutagen). He believed the cat to be killed. Instead, the cat mutated along with two other animals; an owl (Nocturno the Owl) and a crow (Nevermore the Scarecrow). They sought revenge on the chemical plant, and on humans in general by controlling a town with poisoned water. It wasn't until April was stranded in that town with a flat tire, that she called the Turtles for help, and they were able to defeat the trio of mutants.