Romney's cautious approach quickly defined Bain Capital. He worried all the time. "He was troubled when we didn't invest fast enough, he was troubled when we made an investment," Andrews says. "He never wanted to fall short on commitments or representations made to investors."

Quite apart from the swashbuckling era of 1980s corporate deals, where one buyout firm spent only six weeks to hatch a $25 billion takeover, decisions at Bain Capital were tested and retested, debated, discussed, and challenged. Any partner could veto a deal, so the case had to be strong enough to convince them all.

At weekly meetings, Romney took deals apart, found weak spots in the analysis, and argued against going forward. He was so relentless in playing the role of devil's advocate that partner Bob White would later admit to sitting in the meetings occasionally wanting to "punch him in the nose."

By 1986, Bain Capital had invested very little. But that year proved a turning point, with major deals that put the firm on the map. The best known was Thomas Stemberg's office supply company, Staples Inc.

At the time, companies bought most of their pens, pencils and paper from small stationers, usually at significant mark-ups. Stemberg, a former supermarket executive, wanted to change that, but couldn't find investors.

One venture capitalist scoffed at Stemberg, "Why in the world would anyone try to save money on paper clips?"

But Stemberg found someone who would.

Intrigued by the concept, and how it spoke to his inherent frugality, Romney called lawyers, accountants and other professionals to gauge office supply spending, only to conclude Stemberg had overestimated the size of the market.

"Look," Stemberg told Romney, "your mistake is that the guys you called think they know what they spend, but they don't."

Romney and Bain Capital went back to the businesses and tallied up invoices. Stemberg's assessment of the market seemed right after all.

On May 1, 1986, backed by an initial Bain Capital investment of $650,000, the first Staples opened in Brighton. Explosive growth followed. Today, Staples is an $18 billion company.

Bain Capital, meanwhile, enjoyed a nearly sevenfold return when it sold its stake a few years later, reaping more than $13 million from a total of about $2 million invested.

Although Romney would later point to Staples as a key example of the kind of job-creating, forward-looking enterprise he made his living in, venture capital deals like Staples soon became only a small part of his firm's business, in favor of leveraged buyouts.

Venture deals invest in start-ups in the hope they hit it big. Leveraged buyouts combine small amounts of investors' money with large amounts of borrowed money to buy established companies.