As Las Vegas emerged as the epicenter of the U.S. mortgage-default crisis, Jonathan Griffin found a niche as the leading bidder for foreclosed homes in the gambling capital.

Mr. Griffin, who died Sunday at age 27, was a high-school dropout who had worked as a busboy and real-estate agent. His family said the cause of death hadn’t been determined, pending autopsy reports.

Mr. Griffin was an innovator in the booming business of helping investors buy foreclosed homes. His firm, Griffin Group, has offices overlooking a parking lot in downtown Las Vegas where home auctions—known as trustee sales—are held every weekday. He earned fees by providing data on homes headed for auction and related services, and bidding on behalf of investors.

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