Oliver McCarran was a disgraced police officer from New York City, known for helping associates of crime kingpins, including one in league with serial killer Cletus Kasady. After Kasady once again escaped captivity, the latter tracked McCarran down, intending to take his knowledge of the New York Police and the various crime lords around the city. Instead, the Carnage symbiote created a new offspring, which named itself Tarnish.
As the offspring of Carnage, Tarnish is a grandchild of Venom and a sibling of Toxin.