NEW YORK (AP) — Peter G. Peterson's family says the executive and philanthropist who argued passionately that the U.S. must reduce its national debt has died of natural causes. He was 91 years old.

Born to Greek immigrants, Peterson served as CEO of two major corporations over the course of more than 30 years, including the investment bank Lehman Brothers.

He co-founded private-equity firm Blackstone Group with Stephen Schwarzman in 1985. The firm's success made the two billionaires. He also served as commerce secretary during the Nixon administration.

In retirement, Peterson became a prominent voice on the issue of the national debt and government spending. He used his wealth to create the Peter G. Peterson Foundation, an organization focused on reforming entitlement programs such as Medicare and Social Security.