Question: De Selby is a fictional character written by which Irish writer?
Context: Bossy Bear is a fictional character written and illustrated by David Horvath, the co-creator of the popular Uglydoll brand. The Third Policeman is a novel by Irish writer Brian O'Nolan, writing under the pseudonym Flann O'Brien.  It was written between 1939 and 1940, but after it initially failed to find a publisher, the author withdrew the manuscript from circulation and claimed he had lost it.  The book remained unpublished at the time of his death in 1966.  It was published by MacGibbon & Kee in 1967. Rijuda (Bengali: ঋজুদা) is a fictional character written by Buddhadeb Guha.  Rijuda is an adventure enthusiast who explores jungles with his sidekick Rudra and also with Titir and Bhotkai who are the friends of Rudra.  Rudra is the narrator of these stories.  The jungles that he wrote about were mainly in Eastern India.  He first appeared in "Rijudar Songe Jongole", published April, 1973. The most famous 'Rijuda' works are Gugunogumbarer Deshe, Ru aha, Rijuda er Sathe Bauxar Jongole etc.  Rijuda, who was a former hunter, later on became a conservator.  The books of Rijuda teach us a great deal of things about the forests of India and about its beauty.  It also knocks some moral sense into the readers.  Rijuda books are meant for people of all ages. Alysia Yeoh is a fictional character created by writer Gail Simone for the "Batgirl" ongoing series published by DC Comics.  She is Barbara Gordon’s best friend, and a transgender woman.  At the time of her debut appearance, she was noted for being the first major transgender character written in a contemporary context in a mainstream comic book.  The first ever transgender wedding premiered in "Batgirl #45". Peter the Brazen is a fictional pulp character written by George F. Worts under his pen-name Loring Brent.  Peter Moore—his true name—is considered by pulp historians Rick Lai and Will Murray an early inspiration of Lester Dent's character Doc Savage (Dent was an avid reader of "Argosy"). Marty Saybrooke is a fictional character from "One Life to Live", an American soap opera.  The role was originated by Susan Haskell, who portrayed Marty from January 24, 1992, through September 16, 1997, and made brief appearances on February 16, 2004, and February 2005.  Christina Chambers portrayed the role from November 17, 2006, to December 4, 2007, with the character written off for "storyline reasons."  Haskell later returned as Marty on June 11, 2008, and left on June 6, 2011. Gillian Hazeltine is a fictional pulp character written by George F. Worts.  Hazeltine was an attorney/investigator. Sol is a fictional character written for and performed on stage by the Canadian actor Marc Favreau. "De Selby" (spelled "de Selby" in "The Third Policeman" and "De Selby" in "The Dalkey Archive") is a fictional character originally created by Flann O'Brien for his novel "The Third Policeman" in which the nameless narrator intends to use the proceeds of murder and robbery to publish his commentaries on de Selby — a crackpot savant who theorizes, among other things, that the earth is actually shaped like a sausage. Singapore Sammy is a fictional pulp character written by George F. Worts, primarily for "Argosy", one of his primary markets for fiction.  The adventures of Sammy Shay are one of the shorter adventure series characters which Worts wrote (although he penned shorter series, such as his interconnected novelettes which took place in a fictional Florida town called Vingo which were also published in "Argosy").
Answer: Brian O'Nolan