- You may be looking for the Chaos Devil.
The Devil Core was a device created by Dr. Wily and Dr. Eggman and fused with Chaos in order to create the Chaos Devil. Though they experienced some difficulty in doing so, they managed to succeed, gaining a powerful protector in the process. However, their creature proved no match for the mighty Duo, who freed Chaos from the Core's control and crushed it just before all of reality was enveloped by the Super Genesis Wave. (MM: #27, StH: #251)