Dorthea "Doris" Singleton (September 28, 1919 – June 26, 2012) was an American actress, perhaps best remembered as Lucy Ricardo's nemesis/frenemy, Carolyn Appleby, in I Love Lucy. She appeared in two episodes of Hogan's Heroes; How to Win Friends and Influence Nazis as Magda Tischler, and Clearance Sale at the Black Market as Maria.