Susan Thompson Buffett was an American activist for the causes of civil rights, abortion rights and birth control, and the first wife of investor Warren Buffett. She was a director of Berkshire Hathaway, owning 2.2 percent of the company worth about $3 billion at the time of her death, making her the 153rd richest person in the world. Buffett was also president of the Buffett Foundation, which has contributed millions of dollars to educational groups, medical research, family planning groups and other charities.