Armand Douglas Hammer (born August 28, 1986) is an American actor. The son of businessman Michael Armand Hammer and the great-grandson of oil tycoon Armand Hammer, Hammer began his acting career with guest appearances in several television series. His first leading role was as Billy Graham in the 2008 film Billy: The Early Years, and he gained wider recognition for his portrayal of the Winklevoss twins in David Fincher's biographical drama film The Social Network (2010), for which he won the Toronto Film Critics Association Award for Best Supporting Actor.
Hammer went on to portray Clyde Tolson in the biopic J. Edgar (2011), play the title character in the western The Lone Ranger (2013), and star as Illya Kuryakin in the action film The Man from U.N.C.L.E. (2015). In 2017, he starred in Luca Guadagnino's romantic drama Call Me by Your Name, for which he received a nomination for the Golden Globe for Best Supporting Actor. The following year, he portrayed Martin D. Ginsburg in the biopic On the Basis of Sex (2018).