A private U.S. investment corporation few Americans know much about has gained an unlikely starring role in the early stages of the country's 2012 presidential election campaign.

Mitt Romney, a former governor in Massachusetts, is the frontrunner in the race to secure the Republican presidential nomination to oppose U.S. President Barack Obama, a Democrat, in next November's election. Romney has touted his credentials as the founder and former chief executive of Bain Capital, a Boston-based investment firm, and says the experience will help him boost the country's sluggish economic fortunes.

Romney says that Bain, using money from its partners and other investors, bought and nurtured companies that created 100,000 jobs under his leadership from the company's start in 1984 until he left it in 1999.

But now, Romney's Republican political opponents and Mr. Obama's campaign are sharply attacking his Bain tenure. They claim that Romney and his fellow investors were “corporate predators” who, rather than creating successful companies, often fired workers and still gained huge profits when they resold the restructured corporations several years later.

One of Romney's opponents, former House of Representatives speaker Newt Gingrich, said he favors capitalism. But he said Romney at Bain “apparently looted the companies, left people unemployed and walked off with millions of dollars.”

Gingrich supporters have started circulating an anti-Romney video that details several Bain transactions in which workers lost their jobs. Mr. Obama's campaign, which has long assumed Romney will be the president's eventual opponent, has also showcased workers who were laid off after Bain takeovers.

Romney has continued to defend his role at Bain, while acknowledging that not all of the company's investments created successful businesses. But Romney earlier this week unwittingly gave his opponents a new opportunity to showcase Bain's firing of workers when he talked about consumers picking a health insurance company to cover their medical bills. He said he liked to fire anyone who did not serve his needs.

Romney's opponents, including former Utah governor Jon Huntsman, quickly mocked his comment about firing people.

For its part, Bain says it now manages $66 billion in investments for its partners and others. But it is the company's actions more than a decade ago — and Romney's role — that are likely to keep Bain at the forefront of the U.S. political debate.