The Anti-Chaos Nullifier was a device designed by Doctor Robotnik to control the Chaos creature and use him to destroy Sonic the Hedgehog. Robotnik knew that Chaos was uncontrollable but developed the nullifier as an attempt to subdue him. Despite several tests, Robotnik determined that the nullifier would not work but did not destroy it.
Many years later, once Robotnik had met Grimer, Robotnik's faithful assistant discovered the device and decided to use it, hoping to cheer Robotnik up. Unfortunately, Grimer had not found the disappointing test notes and did not the uselessness of the machine. To end all uncertainty, Robotnik destroyed the Anti-Chaos Nullifier and watched as Chaos rampaged through the Metropolis Zone.