Peter L. Bernstein, the author of Against the Gods: The Remarkable Story of Risk and other books, died on June 5th at the age of 90. Bloomberg reported that Bernstein, an economic historian who popularized efficient market theory, died of pneumonia on Friday, the New York Times reported. He was 90 years old and resided in Manhattan.

A financial consultant, Bernstein outlined an investment strategy based on efficient market theory in books including “Capital Ideas” and “Capital Ideas Evolving.”

Instead of just picking stocks that looked like good bets, investors learned from his books to diversify their portfolios using academic equations designed to measure and manage risk, the Times said, quoting Stanford economist William F. Sharpe, who received a Nobel Prize for his work on the new strategy.

“We went from naive and haphazard stock-picking to looking at the whole portfolio in the context of how capital markets operate,” Sharpe told the Times. “Peter Bernstein’s contribution was as an interpreter and communicator, and he certainly did popularize academic finance.”

The hope was that diversification would make the stock market less prone to collapse, the Times said, adding that Bernstein favored more regulation to prevent crashes.

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