Flann O'Brien (5 October 1911 - 1 April 1966) was the pen name of Brian O'Nolan, an Irish novelist and playwright. Born in County Tyrone, he is regarded as a key figure in modernist and postmodern literature. His four English-language novels, At Swim-Two-Birds (1939), The Hard Life (1961), The Dalkey Archive (1964) and The Third Policeman (1967), were published under the pen name Flann O'Brien. His many satirical columns in The Irish Times and an Irish-language novel, An Béal Bocht (1941), were written under the name Myles na gCopaleen.

O'Brien's novels have attracted a wide following both for their unconventional humour and as prominent examples of modernist metafiction. As a novelist, O'Brien was influenced by James Joyce. He was nonetheless sceptical of the "cult" of Joyce, saying "I declare to God if I hear that name Joyce one more time I will surely froth at the gob."