Gwendolyn Sontheim Meyer (born 1961/62) is an American billionaire heiress and equestrian.
She is a great-great-granddaughter of William Wallace Cargill, the founder of Cargill. Her late mother was Marion MacMillan Pictet.
A show jumper, she won the Prix Credit Suisse at the Geneva International Horse Show in 2011. She also sponsors dressage.
She lives in Rancho Santa Fe, California. She is divorced and has two children. As of February 2026, she was estimated to be worth approximately US$5.6 billion.