Lionized as Wall Street’s most capable mop-up man, incoming Merrill Lynch CEO John A. Thain was known as a quiet, polite, and incisive Midwesterner during his days at Harvard Business School.

On Saturday, Thain, a 1979 graduate of Harvard, will take charge of Merrill Lynch and attempt to rescue the brokerage firm from the biggest crisis in its 93-year history.

In interviews with The Crimson, Thain’s former Business School classmates remembered his days across the Charles, where he attended school along with his Merrill Lynch predecessor E. Stanley O’Neal, Labor Secretary Elaine Chao, and eBay CEO Margaret C. Whitman.

James J. Burke Jr., a 1979 graduate of the Business School, said that Thain’s skills were well suited to maneuver Merrill Lynch out of the sub-prime mortgage crisis that has plagued financial firms across the country in recent months.

Thain has gained a reputation as a cordial, perspicacious technocrat who rose to serve as a co-president of Goldman Sachs and revived the ailing New York Stock Exchange.

Merril Lynch reported an $8.4 billion loss in securities and bad loans last month.

Thain was deeply involved in establishing the then-booming mortgage bond business while he was at Goldman Sachs.

“John is an appropriate choice given his background as a risk manager,” Burke said.

Thain’s former roommate, James A. Leahy, remembered Thain as “an unbelievably polite, all-American boy” who was “unassuming in manner” and “genuinely nice.”

“He was the antithesis of what I thought I’d see at the Business School,” Leahy said. “He is one of the best people I’ve ever met in my life.”

Leahy also said that Thain, a graduate of MIT’s electrical engineering program, was mostly known for his intellect.

“I’ve seen no one with the quality of the mind better than John’s,” Leahy said.

“He’s a trained engineer, very good with numbers,” Burke said. “He’s got that kind of mind.”

But what most surprised Thain’s former peers was what hasn’t changed about their Business School classmate.

“He looks exactly the way he did 26 years ago,” said David H. Gaylin ’72, who recognized Thain at a Business School reunion in 2005.

Leahy said Thain, a squash enthusiast, frequently bought fruits and vegetables and was mindful of his health during his days as a student.

“He was the kind of guy who stayed in shape in every aspect of his life,” Leahy said.

One day, Thain accompanied his classmates who were going out to grab burgers. At one point, Leahy recalled, he turned to his friends and said, “‘Why are you guys eating that stuff? That stuff’s bad for you.’”