Marissa Ronson, codenamed "Tweed", was a member of the Spec Ops Echo Six unit sent to Raccoon City during the I-Virus Outbreak. She operated as the demolitions expert. A boyish, highly trained recon specialist with an immense sense of pride. She has a sharp and witty tongue, sometimes to a fault.

At some point prior to 1998, Marissa was an agent for the Secret Intelligence Service, the United Kingdom's secret service-equivalent. An injury sustained during a bomb-disposal operation.