Whitney MacMillan, who led Cargill Inc. for 20 years and was the last member of the founding family to run the agricultural giant, died Wednesday in Vero Beach, Fla., of natural causes.

He was 90.

MacMillan spent 44 years working for the company started in 1865 by his great-grandfather, W.W. Cargill.

A true believer in the idea of moving food from places of abundance to places of scarcity, MacMillan played an instrumental role turning Cargill into a global powerhouse.

"Whitney's almost 20 years as Cargill's CEO defined who we are today. He expanded the company from 31 to 53 countries and quadrupled our employee base," Dave MacLennan, Cargill's current chief executive, said in a statement Thursday.

MacMillan led the Minnetonka-based company through a period of rapid growth and transformation, ultimately moving its executive leadership away from the family. He added independent directors to its board, initiated an employee stock-ownership plan and kept it under private ownership.

When he retired as chairman in 1995, he was the last member of the MacMillan and Cargill families to serve directly as a senior executive operational manager.

MacMillan, who rarely gave interviews, told the Star Tribune upon his retirement that he was confident about Cargill's future but unsure about his impact on it. "I haven't got a clue," MacMillan said. "The proof is 10 years down the pike."

Under his watch, Cargill entered the canola, cocoa, cotton, malt and fertilizer markets and started processing beef and pork, MacLennan said, adding "with our company being the first to adopt a model for the humane treatment of animals."

He was born in 1929 in Orono to Cargill MacMillan and Pauline Whitney MacMillan. He attended the Blake School and Yale University, where he earned a history degree.

MacMillan started working for the family company as a general trainee, rising through the ranks with positions in San Francisco, Minneapolis and the Philippines. He eventually landed in senior management and became chairman and chief executive in 1976, positions he held until retiring.

"When the history of Cargill is complete, Whitney's name will figure prominently as one of the firm's most important leaders," William Pearce, former Cargill vice chairman, said in a statement. "He was an astute businessman and visionary strategist, who provided a critical bridge between the owning families and the company."

MacMillan straddled the fence as both a member of the Cargill family, who collectively own the company, and the executives and board of directors responsible for the company's day-to-day business strategy.

"His job was to maintain the unique commitment of the owning families to the business while developing the evolving management system needed to contend with extraordinary global expansion and to adapt to changing global food needs," Pearce said. "He played that role extremely well."

His brother, Cargill MacMillan Jr., who died in 2011, was also a senior executive at the company. Their father was president of the company in the late 1950s and early 1960s.

Today, Cargill is owned by about 150 family members and is on its seventh generation of shareholders.

With a net worth of $5.1 billion, Whitney MacMillan was listed on the Forbes 400 as the 128th richest American in 2019. With his wife, Betty, MacMillan also supported numerous charitable and educational programs in the Twin Cities and around the country, with a focus on values-based education, health care, the environment and culture.

MacMillan served on numerous boards including the International Peace Institute, the EastWest Institute, the Salzburg Global Seminar and the University of Minnesota's Humphrey School of Public Affairs.

The WEM Foundation he and his wife founded supported dozens of organizations, largely concentrated in Minnesota, Florida and Africa. They included the Guthrie Theater, Smithsonian Institution, Mayo Clinic, Project for Pride in Living and Westminster Presbyterian Church. The foundation also supported conservative-leaning think tanks, such as the American Enterprise Institute in Washington, D.C., and Charlemagne Institute in Bloomington.

In retirement, MacMillan taught corporate strategy at the University of St. Thomas and acted in a number of advisory roles to a number of universities, government agencies and public-policy groups on topics such as global trade and the economy.

"Personally, Whitney served as a mentor to me and many others. He told us to make sure we did everything the right way, with absolute integrity and without fanfare," said MacLennan, who joined Cargill in 1991 and became CEO in 2013.

"His legacy at Cargill is just one chapter in his story of service and impact," he said.