Joseph "Joe" Banks was hit by an unknown type of radiation during a break-in gone bad in a MarsTech laboratory.
Ever since, he seems able to occasionally create a perfect copy of himself, that acts independently from the 'original'. He started taking jobs for criminal elements in Emerald City, calling himself Carbon Copy.
Research has shown that the copies seem to 'decay' after about 2 hours, dying from what seems to be rapid cellular degeneration. This has made it possible to keep track of the original.
The exact source of his powers is still unknown, including the type of energy that allows him to duplicate. Some have suggested that he taps into dark energy, 'recharging' his ability over time.