James Rothenberg, who oversaw Capital Group Co.’s ascent to manager of the world’s largest stock mutual fund before it lost that title to an index fund, has died. He was 69.

Rothenberg, Capital Group’s chairman, died Tuesday of a heart attack, according to an e-mailed statement from the Los Angeles-based mutual fund company, which oversees $1.25 trillion. He was also chairman of Harvard Management Co., which invests the university’s $36.4 billion endowment.

“His intellect, passion and energy were the source of inspiration to all of us and to our more than 7,600 associates worldwide,” Capital Group’s management committee said in the statement. “Our hearts go out to his family and to all who were touched by his extraordinary talents.”

Rothenberg, who joined Capital Group in 1970, oversaw the firm’s growth into a money manager that at its peak owned the world’s biggest mutual fund family, American Funds, and the biggest stock mutual fund, the Growth Fund of America. One of the few investment companies not to fall victim to the technology bubble at the start of the century, Capital Group’s fortunes turned after performance faltered following the 2008 financial crisis and clients flocked to cheaper index funds.

In 2007, Vanguard Group unseated Capital Group as top seller among U.S. mutual funds, and four years later Growth Fund of America lost its top rank to a Vanguard index fund.

Investment ‘Giant’

Throughout those years, Rothenberg remained a staunch defender of active fund management.

“We don’t entirely agree that the answer for all people is indexing,” Rothenberg said in a 2013 interview. “In fact there can be a significant advantage to active investing.”

He became treasurer of Harvard University in 2004 and was also chairman of the board of the Harvard Management Co., which manages the world’s largest endowment. He stepped down as treasurer in 2014.

“He was one of the giants in the investment management world and was part of building Capital Group into one of the premier investment organizations,” Michael Rosen, chief investment officer at consulting firm Angeles Investment Advisors LLC in Santa Monica, California, said in a telephone interview. “He had a legacy that extends beyond Capital Group, to Harvard, and he has had an imprint on the largest endowment in the country.”