A major Republican donor, Mr. Pickens supported Swift Boat Veterans for Truth, which leveled false allegations against John Kerry during the 2004 presidential campaign. Along the way, he had five wives, became a major philanthropist and saw the football stadium at Oklahoma State University, his alma mater, named for him after a donation of hundreds of millions of dollars to the school.

Even in his later years, he never stopped looking for another big score. He bought nearly 400,000 acres of water rights in the Texas Panhandle, hoping to sell that water to Dallas and Fort Worth. And last year he began drilling on his own ranch.

Yet Mr. Pickens’s most lasting impact on business has nothing to do with oil. As a corporate raider in the 1980s, Mr. Pickens — along with men like Carl C. Icahn and Michael Milken — helped develop a shrewd new playbook for making money. He would take a small stake in a public company, call on it to slash expenses and return money to investors, and often pressure the company to sell itself. He was Gordon Gekko before “Wall Street,” and his influence was profound.

That philosophy now shapes the investment decisions of big institutional investors and shareholder activists alike. Depending on whom you ask, it is responsible for the creation of a huge amount of wealth for a great many people, or for a reckless short-term perspective that is widening income inequality and destroying jobs. In either case, it happened, at least in part, because of T. Boone Pickens.

“Today you’re seeing in corporate America a lot of the things that he espoused 30 years ago,” said David Bradshaw, an investment banker at Moelis and Company who is close to Mr. Pickens. “He was ahead of his time.”

Smart and Shrewd

Mr. Pickens was born in Oklahoma’s oil patch in 1928. His father was a landman, buying leases from farmers and selling them to oil companies, and his mother oversaw gasoline rationing for several counties during World War II.