In this case it took a banker to catch a banker. Mr. Cox very quickly realized that GMAC, the mortgage company he was suing in court to save Nicolle Bradbury’s $75,000 house, was mass-producing flawed paperwork to seize people’s homes illegally. This set off what would become known as the robo-mortgage scandal, leading to a $25 billion settlement that forced the nation’s largest banks to halt foreclosures.

For his work, Mr. Cox is one of five people to be awarded a $100,000 Purpose Prize, given to those 60 and over who have created fresh solutions to old problems. The prize, now in its seventh year, has become a sort of MacArthur genius award for people who develop a second career as social service entrepreneurs.

This year’s other $100,000 winners include:

Judy Cockerton, 61, of Easthampton, Mass., a former toy store owner, for creating innovative programs to support foster children.

Lorraine Decker, 64, of Houston, who had a lengthy career as a consultant to Fortune 500 companies, for developing financial education programs aimed at low-income teenagers and adults.

Susan Burton, 61, of Los Angeles, an ex-con and former drug addict, for opening five transitional homes to support women who have been newly released from jail.

Bhagwati Agrawal, 68, of Fairfax, Va., an engineer, for his work in rural India developing systems that produce safe, low-cost drinking water.

The prizes are awarded by Encore.org, a nonprofit organization that develops programs aimed at encouraging retired and older workers to take on second careers in community service. Financing is provided by the John Templeton Foundation and the Atlantic Philanthropies.

This year’s 23 judges included Sherry Lansing, former chairman of Paramount Pictures, David Gergen, Jane Pauley and Sidney Poitier.

While the winners are free to use the $100,000 as they wish, several interviewed said they would use the money to expand their programs.

Mr. Cox, 68, said he plans to use most of his winnings to develop seminars that will train lawyers in Maine to perform consumer protection work.

“Maine is a state with a large rural population where a lot of the attorneys work solo or in two or three person practices,” he said. “Many are unfamiliar with the protections provided under the laws.”

Among other things, he wants to teach lawyers methods for having their legal fees paid by companies that they successfully sue. “A lot of these clients can’t pay much, but their lawyers can recover legal fees from the other side,” Mr. Cox said.

He hopes to bring national experts to Maine to educate the state’s lawyers in consumer protection law.

He also plans to set up a corps of retired lawyers from around the state who will mentor new lawyers and work with them in court.

“The prize money won’t cover the new programs,” he said, “but I’ll use it as seed money, hopefully to raise the $200,000 to $300,000 we’ll need.”

For the last four years he has paid for virtually all the foreclosure work out of his own pocket, he said. “The most I have received was $23,000 in counsel fees for the GMAC case,” he said.

Asked if he intended to use any of the prize money for himself, Mr. Cox said, he might set a little of it aside for a fishing trip.