Eric Mains is fulfilling a dream many Americans have had since the onset of the financial crisis seven years ago: He’s attacking fraud in the banking industry as aggressively as he can, using every possible tool under the law to achieve justice —and win some money back for himself.

Mains, a former team leader with the Federal Deposit Insurance Corporation (FDIC), has become so bitterly embroiled in a six-year dispute with his mortgage lender that he left the regulatory agency, fearing that he might have to eventually name it as a defendant in a federal lawsuit. He’s one of a small yet determined band of people still fighting foreclosure (the seizure of property) cases with obscure and sometimes arcane arguments, built on a simple yet mind-blowing premise: The true ownership of millions of mortgages issued during the housing bubble was fatally corrupted, and now it’s impossible to prove who actually…