Christopher O'Dowd (born 9 October 1979) is an Irish actor and comedian. He received wide attention as Roy Trenneman, one of the lead characters in the Channel 4 comedy The IT Crowd, which ran for four series between 2006 and 2010. He has also starred in several films, Gulliver's Travels (2010), Bridesmaids, Friends with Kids (both 2011), Cuban Fury (2014), Miss Peregrine's Home for Peculiar Children (2016) and The Cloverfield Paradox (2018). He created and starred in the Sky 1 television series Moone Boy, which aired between 2012 and 2015 and brought him Irish Film and Television Award nominations in acting, writing, and directing.

Since 2017, he has appeared as Miles Daly in the Epix comedy series Get Shorty. He had a recurring role on the comedy-drama series Girls. His performance in the British comedy TV series State of the Union won him a Primetime Emmy Award. He made his Broadway debut in the play adaptation of Of Mice and Men in 2014, for which he was nominated for a Tony Award. In 2020, he was listed at number 39 on The Irish Times list of Ireland's greatest film actors. In November 2022, he appeared as the character Philip in the Netflix film Slumberland.