James B. "Jimmy" Lee, the colorful JPMorgan Chase rainmaker whose pioneering work in the loan market helped propel an era of Wall Street deals, died suddenly Wednesday morning. He was 62.

Lee felt shortness of breath while exercising at his home in Darien, Connecticut, and was taken to a hospital, where he died, according to a person briefed on the matter who asked not to be identified discussing personal matters.

"Jimmy was a great friend, leader and mentor to me and so many others," JPMorgan Chief Executive Officer Jamie Dimon said in a statement. "Jimmy was a master of his craft, but he was so much more — he was an incomparable force of nature."

At an investment bank that often emphasized its team and resources over individual stars, Lee was the exception, with a charismatic personality and Rolodex known throughout Wall Street. He had worked for New York-based JPMorgan and its predecessors since about 1975, eventually running its investment bank before becoming a company vice chairman and continuing to garner some of its biggest deals. A rival banker once quipped that one of Dimon's most important tasks every year was to make sure Lee stayed happy.

Lee is survived by his wife, Beth, and three children, Lexi, Jamie and Izzy, according to Dimon's statement.

"It's a sad day for Wall Street," Raymond McGuire, global head of corporate and investment banking at Citigroup Inc., said by phone. "Jimmy Lee was a formidable competitor who commanded respect."

Having built a career making loans and selling bonds, Lee was a primary architect of the modern private equity-industry, pioneering the use of leveraged loans to fund takeovers starting more than two decades ago. Among his most frequent collaborators was Blackstone Group co-founder and CEO Stephen Schwarzman, who worked with Lee on numerous transactions. The two men developed a close friendship.

"Jimmy was a great banker, a tireless mentor and not the least, everyone's favorite golfing partner," said Michael Bloomberg, founder, CEO and majority owner of Bloomberg LP, parent of Bloomberg News. "Most importantly, he was a true friend to so many of us throughout his career. He will be sorely missed and our thoughts and prayers go out to his wife Beth and their daughter and two sons."

Lee counseled some of the biggest dealmakers in corporate America, helping negotiate Comcast Corp.'s acquisition of NBC from General Electric Co. in 2009, the United-Continental airline merger in 2010 and General Motors Co.'s $18 billion initial public offering later that year. He was also an adviser to Dell Inc. on its $24.4 billion buyout by its founder Michael Dell.

He was advising GE on the sale of its financial arm — part of the transformation of the company by CEO Jeff Immelt.

Lee was an adviser to Alibaba Group Holding Ltd. on its IPO last year — a $25 billion deal that was the largest ever — after building a relationship with co-founders Jack Ma and Joe Tsai. At a party in New York the day the shares began trading, Lee introduced Ma to a crowd of hundreds.

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