Katherine Tanner owns an estimated 3% stake in Cargill, the largest food company in the world. She's one of four billionaire sisters who inherited stakes in the company from their father W. Duncan MacMillan, who died in 2006. Her great-great-grandfather, W.W. Cargill, founded the business as a single grain warehouse on the end of an Iowa railroad line in 1865. The family still owns roughly 90% of Cargill, which did $110 billion in 2017 sales across food, agriculture, financial and industrial divisions.