Sir George Iain Duncan Smith, often referred to by his initials IDS, is a British politician who served as Leader of the Conservative Party and Leader of the Opposition from 2001 to 2003. He was Secretary of State for Work and Pensions from 2010 to 2016. He has been Member of Parliament (MP) for Chingford and Woodford Green, formerly Chingford, since 1992.

Duncan Smith was born George Ian Duncan Smith on 9 April 1954 in Edinburgh. A second "i" was added to his middle name "Ian" later in life, with several explanations given: Duncan Smith changed it himself to prove that he was committed to Scotland; the person who filled in his birth certificate made a mistake; Duncan Smith's mother registered him, but Duncan Smith's patriotic father later suggested to his son to change it to the Scottish spelling.

Duncan Smith married Elizabeth "Betsy" Fremantle, daughter of the 5th Baron Cottesloe, in 1982. The couple have four children and live in a country house belonging to his father-in-law's estate in Swanbourne, Buckinghamshire. He is a Roman Catholic. He has been reported to support both Tottenham Hotspur, where in 2002 he held a season ticket and Aston Villa.