Piers Anthony Dillingham Jacob (born 6 August 1934 in Oxford, England) is an English American author in the science fiction and fantasy genres, publishing under the name Piers Anthony.
 He is most famous for his set in the fictional realm of Xanth.
Well-Tempered Clavicle is the 35th book of the Xanth series by Piers Anthony.
 The title is a pun on the Bach musical work "The Well-Tempered Clavier."
Xanth ( ) is a fantasy world created by author Piers Anthony for his "Xanth" series of novels, also known as "The Magic of Xanth".
 Anthony originally intended for Xanth to be a trilogy, and after the success of the first three books expanded the series to nine books.
 A devoted fan base persuaded the author to continue writing the series, which is now open-ended.
The Source of Magic is a fantasy novel by British-American writer Piers Anthony, the second book of the Xanth series.
 This novel begins one year after the events of "A Spell for Chameleon", and describes the adventures of Bink after he has settled down with his pregnant wife, Chameleon.
 King Trent had appointed Bink the Official Researcher of Xanth at the end of the previous book, and given him the task to discover Xanth's source of magic.
 After many hazards, Bink and his companions succeed but Bink makes a moral choice that ends up destroying the magic of Xanth.
Currant Events is the twenty-eighth book of the Xanth series by Piers Anthony, and the first book in the second Xanth trilogy.
Castle Roogna is a fantasy novel by British-American writer Piers Anthony, the third book of the Xanth series.
 The castle itself is also the residence of the present King of Xanth.
Xanth is a fictional universe created by author Piers Anthony.
 It is a magical land most often described as being shaped like the state of Florida.
 The geography of Xanth is, therefore, very similar to that of Florida.
 As is typical with the series, many geographical landmarks are puns based on real-world locations.
 As an example, the "With-A-Cookie River" in Xanth is roughly parallel with the Withlacoochee River in Florida.
Arthur Annesley Ronald Firbank (17 January 1886 – 21 May 1926) was an innovative English novelist.
 His eight short novels, partly inspired by the London aesthetes of the 1890s, especially Oscar Wilde, consist largely of dialogue, with references to religion, social-climbing, and sexuality.
Companions of Xanth is an adventure game published in 1993 by Legend Entertainment.
 The game is based on Piers Anthony's Xanth novels and loosely follows the plot of his novel "Demons Don't Dream", in which a young man uses a computer game to enter and explore the world of Xanth.
Air Apparent is the thirty-first book of the Xanth series by Piers Anthony, which was first mentioned in the "Author's Note" in "Currant Events".
 Piers Anthony stated that notions from his readers have already been set aside for use in this installment in the same "Author's Note."

Question: In between Ronald Firbank and Piers Anthony who is most famous for his set in the fictional realm of Xanth?
Answer: Piers Anthony Dillingham Jacob