Gwendolyn Sontheim Meyer (born 1961/62) is an American heiress and equestrian.
She is a great-great-granddaughter of William W. 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 on Coral Reef Ranch in Rancho Santa Fe, California. She is married, and has two children. As of March 2012, she was estimated to be worth approximately US$3 billion.