Duperreault “re-entered” the Bermuda market in 1994—just at the time when Bermuda was seeing a huge influx of reinsurance capital following Hurricane Andrew—when he became chairman, president and CEO of Ace Insurance.

Why re-entered? Duperreault was born in Bermuda, a fact he says he deliberately kept to himself at first while being considered for Ace’s top executive position.

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After more than 20 years at American International Group (AIG), where he held numerous positions before being named executive vice president of AIG Foreign General Insurance and chairman/CEO of AIG’s American International Underwriters (AIU), he wanted to earn the Ace position on his own merits.

“I didn’t want the board to know I was a native; I didn’t want to get the job based on that,” he reveals. “I told them I was ‘born to do the job,’ and they asked me, ‘What does that mean?’ and [eventually] I told them.”

The task was to transform Ace, which at that time was a Bermuda specialty carrier, into a global insurance organization.

That goal was achieved as Ace expanded aggressively under Duperreault’s watch, acquiring Bermuda-based property-catastrophe reinsurance companies Tempest Re in 1996 and CAT Limited in 1998.

But the most notable deal Duperreault executed was taking control of Cigna P&C in 1999, a game-changing move that he says “changed the company forever.”

The Cigna acquisition played a pivotal role in growing Ace from an operation of about 50 employees (“I was 55th,” Duperreault recalls) into a Top 20 underwriter with more than 16,000 people working in 53 countries today.

In addition to changing the company, the Cigna deal “was transformative for me personally; I learned so much during that process,” he says.

“One thing I learned was the power of communication, the power of being forthright, being straight. As soon as we closed the deal, we went around the country to the cities Cigna was in and said, ‘We’re going to have to downsize.’ I told them what I liked and didn’t like about the company—that not everything’s perfect, things have to change. What surprised me was the [positive] reception I received.

“That was a big eye-opener for me,” he says. “People just want to know the truth. A lot of the people working [in an organization] see the problems; they see it clearer than management does. They just want someone to fix it.

“There’s an old cliché that anything is possible, and before [the Cigna deal] I would have been skeptical of that,” he adds. “But I learned that if you have the motivation and support, don’t set your sights low. Set them as high as you possibly can.”

Duperreault’s role in growing Ace into a major international player, and the credit he can take for establishing Bermuda as a key cog in the global insurance machine, would have been enough to earn him legendary status.

But in 2008, Duperreault was asked to come out of his brief retirement (he had served as Ace’s CEO until 2004 and remained on as chairman until 2007) to head up global brokerage giant Marsh & McClennan Cos. (#231 on the Fortune 500) as its president and CEO, a position he still holds—and one he describes as “a calling” to which he couldn’t say no.

In 2008, Marsh was still dealing with morale and reputational issues following the investigation into contingent commissions led by then-N.Y. Attorney General Eliot Spitzer—and the massive fines and leadership shake-up that resulted. To right the ship, the firm wanted at the helm someone with both extraordinary industry experience and unquestioned integrity.

Duperreault was the perfect choice.

“I was happily retired—I really was,” he recalls. “I wasn’t looking for work, frankly. I’d obviously known [Marsh] as long as I’d been in the business, and I’d always had enormous respect for it and its people. It was a company I wanted to help get back to where it belonged in the first place, so it was an easy decision.”

“The versatility of Brian’s strengths as an executive are hard to overstate,” says Cliff Gallant, managing director at Keefe, Bruyette and Woods, who referred to Duperreault as “a great pick” and “highly respected” when Marsh announced the appointment.

“At Ace, he had fantastic vision and was able to take a startup Bermudian, something which is quite commonplace, and through some daring and boldness he created what is now one of the world’s most respected insurance franchises,” Gallant adds. “Then, he was able to take the lead of a very different type of business, a broker and consultant, and revitalize MMC from a dark period of desperation to again be the world’s blue-chip risk-management leader.”

Insurance remains “a fascinating business,” says Duperreault. “You wouldn’t have an economy without an insurance business. It’s nice to go to work and do something important.

“It requires what they used to call Renaissance Men—people who know a variety of subjects,” he says. “You have to be quantitative. You have to be curious. You have to be aware how information is used, from retrieval to modeling. You have to be able to take a risk, say yes and live with it for a long time. You have to have a love for dealing with people—and be able to know who’s telling the truth and who isn’t.”