ONE OF THE MOST INFLUENTIAL MEN IN AMERICAN HISTORY:

Mr. Johnson led the Boston investment giant for about four decades, helping grow the sums Fidelity invested for customers from $3.9 billion to $4.5 trillion. In a city known for its many financial companies, Fidelity towered above them all under his leadership. [...]

A fiercely competitive businessman, he remained famously modest in public appearance and demeanor throughout his life -- walking from his Beacon Hill home to Fidelity's downtown offices for many years -- and he professed little interest in his personal wealth.

"That isn't what turns the motor," Mr. Johnson said in a rare interview with the Globe in 1994. "The best thing about obviously having a large cash flow is that you can invest it in a lot of other things that produce something else that has value to us and value to other people."

Mr. Johnson spent hundreds of millions of dollars on philanthropic causes, with a particular interest in art and medical research. Known as a generous benefactor with no concern for the public relations value of giving away money, he was often identified simply as AD - anonymous donor - when charities acknowledged many of his gifts.

Mr. Johnson and his family's foundation were major supporters of the Museum of Fine Arts in Boston, where his wife, Elizabeth "Lillie" Johnson, was an active honorary trustee for many years, and of the Peabody Essex Museum in Salem. He launched a separate foundation to acquire American and Asian antiques, which were loaned to museums and historical societies for public viewings.

Among medical causes, Mr. Johnson was especially interested in research into Alzheimer's disease, an affliction that took his father's life in 1984. He quietly launched his own nonprofit, the Alzheimer Research Forum Foundation, which acts as an online clearinghouse of information.

Mr. Johnson also launched Fidelity Charitable. The business unit manages thousands of accounts from which customers can send donations. It became the largest nonprofit fund-raiser in the country, outpacing the United Way in 2016.

Mr. Johnson spent extensively on computers and technology that enhanced the company's reputation for strong customer service. In the early days, he reached out to customers with a blizzard of advertising and made it easy for shareholders to call Fidelity for help with toll-free numbers staffed around the clock, a big change in a business that grew out of the discreet and conservative world of trusts and private bankers.

For many years, he continued his father's practice of hiring bright, young money managers at Fidelity and encouraging them to take investment risks, again contrary to a common industry practice that emphasized group decisions by older men.

This new investment culture produced many stars -- none more famous than Peter Lynch -- and established Fidelity as home to some of the hottest mutual fund managers just when one of the great bull markets in history got underway, in the early 1980s.

"He was a radical egalitarian despite the fact that he was born into an upper-class Boston Brahmin family," said Bob Pozen, a top Fidelity executive who left the company in 2001. "He just wanted to hire the best people."

As Fidelity's investment management business grew, Mr. Johnson diversified the company into other ventures. He built a booming discount brokerage subsidiary and a large real estate business that redeveloped the World Trade Center and built a hotel across the street on the South Boston waterfront. 

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