BOSTON — When Mitt Romney’s record at Bain Capital first came under assault, his beleaguered campaign staff turned to Bob White, an informal adviser. He quickly recruited researchers to conduct a deal-by-deal autopsy, searching for uplifting examples to share with voters to counter rivals’ accounts of exploitative ones.

When Romney’s team of longtime aides risked becoming insular, White navigated a minefield of office politics to ensure that Ed Gillespie, a veteran Republican operative brought in from the outside, had a major hand in strategy decisions.

And when Romney was portrayed as a robotic Mr. Fix-It, unwilling to tell his personal story, White pushed to recast him as a compassionate church leader, selfless neighbor and adoring father.

White, a former college hockey player with a pronounced Boston accent, has emerged as a singular force within the Romney campaign. A designated troubleshooter and in-house consultant, he helped steady a wobbly candidacy and reverse its trajectory in recent weeks, according to interviews with a dozen Romney aides and advisers.

Little seen and little known to the public, White — a multimillionaire businessman who has the nebulous title of campaign chairman and accepts no salary — plays an outsize role. Variously described by aides as the candidate’s alter ego, his aide-de-camp, his genial enforcer and his gut check, White gained his stature entirely through his long relationship with Romney, who hired him 31 years ago for a management consulting job. His place in a Romney White House, should there be one, is all but guaranteed.

“Bob’s voice in Romneyworld carries enormous weight, both internally and externally,” said Spencer Zwick, the campaign’s finance chief. “People crave his approval and his sign off. They know Mitt listens to him.”

White, 56, jokes that his job is “Friend of Candidate.” Romney calls him “my wingman.”

Their partnership is devoted and durable, with Romney relying on White as an informal adviser at every stage of his career: Bain, the Massachusetts governorship, the Olympics and both presidential campaigns.

Inside a campaign that long favored hammering on President Barack Obama and playing down the details of Romney’s biography, White has pushed for transparency, arguing that the benefits outweighed the risks. He advocated that Romney discuss his Mormon faith, publicly embrace his financial success and release his recent income taxes, taking to a white board to tutor a campaign media relations team befuddled by the candidate’s far-flung investments and trusts.

Aides, who say nothing in the campaign is achieved without exhaustive consensus, said Romney’s emergence in the final stretch of the race as a moderate-sounding pragmatist, talking about his charitable acts, business career and record as governor, bore White’s fingerprints.

He “wants people to see the Mitt Romney he knows,” said Ron Kaufman, a top campaign adviser. “He wants to give people a reason to go to the polls.”

Neither White nor Romney would talk for this article about their relationship. But by granting White access to every meeting and any aide, Romney has revealed something about his own leadership style, suggesting the limits of his faith in political operatives and his enduring belief in the problem-solving powers of fellow management consultants.

At Romney for President headquarters here, White peppers advisers with provocative questions, tests their assumptions and challenges their plans, just as he and Romney did at Bain Consulting.

“Why are we running this ad now?” he has asked. “Is this the best use of money?”

White may not apply the same clear-eyed scrutiny to his friend the candidate, though, that he does to campaign operations. At least publicly, he speaks of Romney with near-reverence, unable or unwilling to find fault.

White, a silver-haired father of six, has a barking laugh and an easy grin. His lucrative career at Bain, where he is still an investor, has given him the freedom to help out Romney and pursue enthusiasms, like his part ownership of the Boston Celtics. But he grew up far from the wealthy Michigan suburbs and elite prep schools of Romney’s youth.

The son of an Irish-Catholic factory machinist and a telephone service representative in Woburn, Mass., he was the first member of his family to attend college — Bowdoin, on financial aid. He was the goalie on the hockey team, “which at Bowdoin is like being the starting quarterback on a college football team,” said David Binswanger, a classmate.

But White stood out for blending in, splitting his time between the jocks and the A students.

“You would have expected somebody like that to be the ego, or the big man on campus,” Binswanger said.

That understated quality, colleagues said, drew Romney to him. After recruiting White to Bain Consulting in 1981, Romney made him the first employee of Bain Capital, the private equity firm he founded three years later. White’s trademark, then and now: making change without making waves. Respected and well liked, White generally gets his way.

Campaign aides said White has pulled off the tricky job of being Romney’s close friend while earning the trust of the candidate’s staff, by making clear that much of what he learns will remain confidential. He works from an office on the second floor of the Romney campaign office in Boston’s North End, where a white board is covered in handwritten charts.

But he is frequently on the road, sitting a row behind Romney on the candidate’s plane, offering jokes and counsel. He has a knack for figuring out when Romney is feeling disconnected from headquarters and should be looped in on a conference call, or when he needs a break in his tight schedule.

And if Romney makes it to the White House? White is on the team planning the transition, and aides cannot imagine that Romney would not turn to him again.

White has at least contemplated a role for himself in the capital. Back in the 1990s, he interviewed a job candidate at Bain Capital named Marc Walpow, who said he had asked White what he wanted to do after his time at the firm. Walpow still remembers his answer: “I might go to Washington with Mitt.”