Flann O'Brien was the pen name of Brian O'Nolan (Brian Ó Nualláin in Irish), an Irish novelist and satirist, born on October 5, 1911, and passed away on April 1, 1966. He is considered a key figure in twentieth-century Irish literature. Working as a civil servant by day, O'Nolan wrote under various pseudonyms, with Flann O'Brien and Myles na gCopaleen being his most well-known. His English-language novels, such as "At Swim-Two-Birds" and "The Third Policeman," are celebrated for their wit, inventiveness, and complex play on language and narrative structure. He also wrote a long-running satirical column in the Irish Times under the name Myles na gCopaleen, which offered a humorous and critical reflection on Irish life and politics. O'Brien's work is often associated with modernist and postmodernist literature and continues to influence writers and readers worldwide.