As courts across the country face a wave of foreclosures, a name little known to the public has cropped up on thousands of court filings as a stand-in for prominent banks, lenders and mortgage servicers. 

Mortgage Electronic Registration Systems, headquartered in a nondescript office building in Reston Town Center, has flourished quietly over the past decade, saving financial firms hundreds of millions of dollars by helping them avoid the time and expense of filing mortgage documents and paying fees each time a loan changes hands.