An Béal Bocht (Irish: "The Poor Mouth" ) is a 1941 novel in Irish by Brian O'Nolan (Flann O'Brien), published under the pseudonym "Myles na gCopaleen".
 It is widely regarded as one of the greatest Irish-language novels of the 20th century.
 An English translation by Patrick C. Power appeared in 1973.
 Stan Gebler Davies wrote: ""The Poor Mouth" is wildly funny, but there is at the same time always a sense of black evil.
 Only O'Brien's genius, of all the writers I can think of, was capable of that mixture of qualities."
At Swim-Two-Birds is a 1939 novel by Irish writer Brian O'Nolan, writing under the pseudonym Flann O'Brien.
 It is widely considered to be O'Brien's masterpiece, and one of the most sophisticated examples of metafiction.
Lillian Maxine Serett (1924-1994), also known as Maxine Sanini and Maxine Savant, born Lillian Maxine Harrison in Groveton, Texas, January 28, 1924, an author and lecturer on sex and sex techniques.
 She is best known as the author of "The Housewife's Handbook on Selective Promiscuity", the only book ever to be banned by the United States Supreme Court.
** When she was 36 and wrote the book, her legal name was Lillian Maxine Savant, but she wrote under the pseudonym of "Rey Anthony".
 The resulting court case, Ginzburg v. United States, resulted in Ralph Ginzburg serving six months in federal prison for publishing the book, but Savant, the author, was never prosecuted.
 "Maxine Serett" was an assumed name she took on only for the trial.
 At the time of her death from a massive heart attack at age 70 in Pasadena, Texas,** she had been using the assumed name Maxine Sanini for more than two decades.
 An ebook of "Housewife's Handbook on Selective Promiscuity," subtitled "Definitive Edition," edited by Toni Savant, one of Serett's five daughters, and containing a biography of the author, was published and posted on Amazon.com on May 26, 2012.
Brian O'Nolan (Irish: "Brian Ó Nualláin" ; 5 October 1911 – 1 April 1966) was an Irish novelist, playwright and satirist, considered a major figure in twentieth century Irish literature.
 Born in Strabane, County Tyrone, he is regarded as a key figure in postmodern literature.
 His English language novels, such as "At Swim-Two-Birds", and "The Third Policeman", were written under the "pen name" Flann O'Brien.
 His many satirical columns in "The Irish Times" and an Irish language novel "An Béal Bocht" were written under the name Myles na gCopaleen.
Oswell Blakeston was the pseudonym of Henry Joseph Hasslacher (1907–1985), a British writer and artist who also worked in the film industry, made some experimental films, and wrote extensively on film theory.
 He was also a poet, and wrote in non-fiction areas including travel, cooking and pets.
 His pseudonym combined a reference to the writer Osbert Sitwell with his mother's maiden name.
Mars is an autobiographical book by Fritz Angst (1944 – 1976) under the pseudonym Fritz Zorn.
 It was first published in 1977.
 Adolf Muschg wrote its long and engaged foreword.
 The book was reviewed in the book review section of New York Times, which says that the author's pseudonym of "Fritz Zorn" literally means "Angry Fritz".
Alfred William Pullin, known by the pseudonym Old Ebor (30 July 1860 – 23 June 1934), was a British sports journalist who wrote primarily about rugby union and cricket.
 He wrote mainly for British newspapers the "Yorkshire Post" and the "Yorkshire Evening Post".
 Considered by critics to be one of the greatest authorities in the country on his two sports, he wrote a daily column using his pseudonym "Old Ebor" for 40 years.
 Most often associated with his reporting on Yorkshire County Cricket Club, he has been credited as defining the role of a sports journalist.
 Two of his most widely known works were on cricket: "Talks with Old English Cricketers" and "History of Yorkshire County Cricket, 1903–23".
Douglas A. Mendini (1953-2016) was an author who wrote under the pseudonym Julian Biddle, known for "What Was Hot", a history of pop culture in America, among other books.
 The name was a pseudonym for writer Douglas A. Mendini (1953-2016).
 Writing as Mendini, his non-fiction appeared in Life, Entertainment Weekly, and Country Living magazines, among others.
 He was also the playwright of “A Good Sport”, “Overeating Causes Death” and other plays.
 His fiction appeared in over 30 journals.
The Bluebird Books is a series of novels popular with teenage girls in the 1910s and 1920s.
 The series was begun by L. Frank Baum using his Edith Van Dyne pseudonym, then continued by at least three others, all using the same pseudonym.
 Baum wrote the first four books in the series, possibly with help from his son, Harry Neal Baum, on the third.
 The fifth book is based on a fragment by Baum and written by an unknown author.
 The last five books were written by Emma Speed Sampson.
 The origin of the title is uncertain, but the books were all published in hardcover with blue cloth.
Emily Devenport is an American science fiction writer, known for the six novels she wrote under her name, the one novel written under the pseudonym Maggy Thomas and the two novels set in the fictitious Belarus planet that she wrote under the pseudonym Lee Hogan.

Question: What was the pseudonym of the author of At Swim-Two-Birds when he wrote "An Béal Bocht"?
Answer: Myles na gCopaleen