Justin Paul Theroux (; born August 10, 1971) is an American actor, film producer, comedian, and screenwriter. He is known for his work with film director David Lynch in Mulholland Drive (2001) and Inland Empire (2006), his starring role as Kevin Garvey in the HBO series The Leftovers (2014–2017) and as Tom in The Girl on the Train (2016).

He is also known as a screenwriter for films such as Tropic Thunder (2008) and Iron Man 2 (2010).