Sienna Rose Diana Miller (born 28 December 1981) is a British-American actress, model, and fashion designer.
In 2008, she was nominated for the BAFTA Rising Star Award, while for her role as Tippi Hedren in the 2012 TV film The Girl, she was nominated for a BAFTA TV Award for Best Actress and a Golden Globe Award for Best Actress. Her film roles include the crime thriller Layer Cake (2004), the comedy Alfie (2004), the biopic Factory Girl (2006), the drama The Edge of Love (2008) and the military science fiction action film G.I. Joe: The Rise of Cobra (2009). In 2014, she starred in two biographical dramas, Foxcatcher, playing Nancy Schultz, and American Sniper, portraying Taya Renae Kyle.
Born in New York City, United States, Miller moved to London with her family when she was just over a year old. Her mother, Josephine, is a South African-born English former model. Her father, Edwin Miller, is an American banker turned dealer of Chinese art. Miller has a sister, Savannah, and two half-brothers, Charles and Stephen, as well as a step brother, Tanner. Miller attended Heathfield School, Ascot, a boarding school in Ascot, Berkshire, and later studied for a year at the Lee Strasberg Theatre and Film Institute in New York City. She carries a British passport.