Drucker died of natural causes at his home in Claremont, east of Los Angeles, said spokesman Bryan Schneider.

Drucker was considered a management visionary for his recognition that dedicated employees are key to the success of any corporation, and marketing and innovation should come before worries about finances.

His motivational techniques were used by executives at some of the biggest companies in corporate America, including Intel Corp. and Sears, Roebuck & Co.

In 2002, Drucker was awarded a Presidential Medal of Freedom. He has been called "the world's foremost pioneer of management theory" and a champion of concepts such as privatization, management by objective and decentralization. Business Week magazine hailed him as "the most enduring management thinker of our time," and Forbes magazine featured him on a 1997 cover under the headline: "Still the Youngest Mind."

In the early 1940s, General Motors invited Drucker to study its inner workings. That experience led to his first management book, "Concept of the Corporation," in 1946. He went on to write more than 30 books.

"He's very much an intellectual leader, and that's not common," said D. Quinn Mills, a professor at Harvard Business School who shared the podium at several conferences with Drucker. Quinn described Drucker's insights as rare.

After the big stock market decline of October 1987, Drucker said he had expected it, "and not for economic reasons, but for aesthetic and moral reasons."

"The last two years were just too disgusting a spectacle," Drucker said. "Pigs gorging themselves at the trough are always a disgusting spectacle, and you know it won't last long."

Drucker termed Wall Street brokers "a totally non-productive crowd which is out for a lot of easy money."

"When you reach the point where the traders make more money than investors, you know it's not going to last," he said.

"The average duration of a soap bubble is known. It's about 26 seconds," Drucker said. "Then the surface tension becomes too great and it begins to burst.

"For speculative crazes, it's about 18 months."

Drucker was born in Vienna, and educated there and in England. He received a doctorate in international law while working as a newspaper reporter in Frankfurt, Germany. He remained in Germany until 1933, when one of his essays was banned by the Nazi regime. For a time, he worked as an economist for a bank in London, then moved to the United States in 1937.

He taught politics and philosophy at Bennington College in Vermont and for more than 20 years was a professor of management at New York University's graduate business school.

Beginning in 1971, he taught a course for midcareer executives at Claremont Graduate School in California, which named its business school after him.

His management books included: "The Effective Executive," 1966; "Management: Tasks, Responsibilities, Practices," 1974; and "Managing in a Time of Great Change," 1995. In 2004, he put out "The Daily Drucker: 366 Days of Insight and Motivation for Getting the Right Things Done."

He also wrote scores of articles for the academic and popular press, and two novels and a 1979 autobiography, "Adventures of a Bystander."

While much of his career was spent studying employees in the workplace, he also dedicated time to the service sector, founding the New York-based Peter F. Drucker Foundation for Non-profit Management, known since 2003 as the Leader to Leader Institute.

Jack Beatty, a senior editor at Atlantic Monthly magazine who wrote the book "The World According to Peter Drucker," described the management guru as "uproariously funny (with) a great rapport. You ask him a question and it can go on for some time."

Drucker is survived by his wife, Doris, and their four children, Claremont said.