Gillian Leigh Anderson OBE (born August 9, 1968) is an American actress, writer, and activist. She is best known for her roles as FBI Special Agent Dana Scully in the sci-fi series The X-Files (1993–2002; 2016–2018), Lily Bart in the drama film The House of Mirth (2000), DSI Stella Gibson in the BBC/RTÉ crime drama series The Fall (2013–2016), Jean Milburn in the Netflix comedy-drama series Sex Education (2019–2023), and Margaret Thatcher in the fourth season of the Netflix drama series The Crown (2020). She has won two Primetime Emmy Awards, two Golden Globe Awards, and four Screen Actors Guild Awards.

Born in Chicago, Anderson was raised first in London and then in Grand Rapids, Michigan. She later started her career onstage in New York City before achieving international recognition for her work on The X-Files. Her film work includes the dramas The Mighty Celt (2005), The Last King of Scotland (2006), Shadow Dancer (2012), and Viceroy's House (2017), as well as the X-Files films Fight the Future (1998) and I Want to Believe (2008). Her television credits include Lady Dedlock in Bleak House (2005), Wallis Simpson in Any Human Heart (2010), Miss Havisham in Great Expectations (2011), Dr. Bedelia Du Maurier on Hannibal (2013–2015), Media in the first season of American Gods (2017), and Eleanor Roosevelt on The First Lady (2022).