Susan T. Buffett, the wife of billionaire investor Warren Buffett (search), died Thursday of a stroke at age 72, the company said.

Buffett, chairman of Berkshire Hathaway (search) and a hugely influential investor, was with his wife when she died in Cody, Wyo., where they were visiting friends, the company said. She had been admitted to West Park Hospital in Cody the night before, a hospital spokeswoman said.

Susan Buffett, a Berkshire director, was listed this year by Forbes magazine as the 60th richest American, with a personal net worth of $3.1 billion.

Though the Buffetts had lived separately for many years, she had also stood to inherit her husband's fortune. Warren Buffett, second only to Bill Gates (search) on the Forbes world wealth list, had said his Berkshire stock, valued at about $42.9 billion, would go to his wife upon his death and then to a foundation.

She had been treated last fall for mouth cancer, and doctors had said she was doing well following the surgery and radiation therapy.

It was announced last week that the couple donated $6 million to five California medical specialists who coordinated her treatment.

Buffett and his wife married in 1952. After they separated, she spent much of her time in San Francisco, but they often traveled and spent time together.

The Buffetts had three children: Susie, 50, who lives in Omaha; Howard, 49, who lives near Decatur, Ill., and who also is on Berkshire's board; and Peter, 46, who is a musician living in Milwaukee.

Warren Buffett took $100 from his own pocket in 1956 and turned it into a multibillion-dollar company. He built his empire on a simple business philosophy of investing in brand-name companies that he understands, including Dairy Queen and Coca-Cola Co. (KO).