A Cerberus or Zombie Dog is a enemy from the Resident Evil series. It is a Doberman that has been infected with the T-Virus. These dogs usually have parts of their internal organs and rib cage partially exposed. Although the terms Cerberus and Zombie Dog are usually used interchangeably, there is a difference between a Cerberus and Zombie Dog.
A Cerberus was used as a subject by Umbrella to test the effects of the T-Virus. They were given the code number MA-39 and were named after the mythological three-headed guardian of Hades. They were seen in the Arklay Research Facility (in Resident Evil) and running loose in the Arklay forest area. Several were also being transported within the Ecliptic Express (in Resident Evil 0) inside the train's Freight Car.
Zombie Dogs were created through accidental exposure to the T-Virus as a result of a viral outbreak. The Zombie Dogs seen in Raccoon City (in Resident Evil 2 and Resident Evil 3: Nemesis) were police dogs that ate contaminated dog food and became zombies. The Zombie Dogs in the Rockfort Island Military Training Facility (in Resident Evil Code: Veronica) were military dogs used by Umbrella's Special Forces. Of these, most only experience skin necrosis, exposing their musculature. Aggression is also increased, making them exceedingly dangerous.