He turned a tiny family business into a billion-dollar weight-loss empire by replacing calorie counting and forbidden foods with “just add milk.”

He helped pioneer a branch of the field that exposed hard-wired mental biases in people’s economic behavior. The work led to a Nobel.

He led the company from 1977 to 1993 and helped transform Wall Street into a more competitive financial marketplace.

He was chairman of the New York Stock Exchange and rose to lead the venerable securities firm Kidder, Peabody, but stepped down after it was…