In the works of Dorothy L. Sayers, the fictional title of Duke of Denver is held by Gerald Wimsey, older brother of the books' protagonist, Lord Peter Wimsey. In novels written after Sayers' death by Jill Paton Walsh (with the cooperation of the Sayers estate), Lord Peter also eventually holds the title. Sayers and several friends constructed an elaborate backstory for the duchy.
In Sayers's works
Novels
In Sayers's stories, Lord Peter was the second of the three children of Mortimer Wimsey, 15th Duke of Denver.
The duchy, Wimsey's mother the dowager duchess, and his brother Gerald Christian Wimsey, the then Duke of Denver, were introduced in Sayers's first Wimsey novel, Whose Body?.
The 1935 second edition of Sayers's second novel, Clouds of Witness, included a fictitious entry from Debrett's Peerage that described the Wimsey coat of arms. In it, Gerald is charged with murder. Gerald refuses to supply an alibi for himself, is tried by his peers, before the full House of Lords, and eventually acquitted through his brother's efforts. Gerald is characterized, in the words of Mary McGlynn (professor of English at the City University of New York), by his idiolect, his "crude word choices, chatty asides, illogical sequencing, and missing letters". Although in the words of his brother he is "a shocking ass", the character of Gerald is portrayed with a degree of sympathy, with his fictional uncle describing him as having "more sense of responsibility than I expected" and his reaction to Peter's marriage to Harriet being a favourable one.
Gerald's wife Helen, Duchess of Denver, is pilloried throughout the novels, and in the opinion of Eric Sandberg (professor of English at the City University of Hong Kong) is the least pleasant character in them short of the actual murderers themselves, and even some of the latter are portrayed more sympathetically than Helen Denver is. Her letter in the opening of Busman's Honeymoon presents her as completely misunderstanding the relationship between Peter and Harriet, and she repeatedly patronizes and insults Harriet according to entries from her mother-in-law's diary. Her angry reaction to Peter and Harriet evading her interference in their wedding is echoed in another character's description of her as "a tartar, very cross, and as stiff as a poker"; and a later backhanded compliment in the novel states that "To do her justice, I can't see she could have found anything nastier to say if she'd thought it out with both hands for a fortnight.".
In The Attenbury Emeralds, written by Jill Paton Walsh in 2010 with the cooperation of Sayers' estate, Gerald dies in 1951 from a heart attack during a fire at Duke's Denver. Because his son, Viscount St. George (a fighter pilot), did not survive the Second World War, Lord Peter inherits the title.
The fictional estate of the duchy is Duke's Denver, with the ancestral home being Bredon Hall, situated east of the real village of Denver, Norfolk. In the first novel it is where Wimsey is taken by his mother for rest and recuperation, and Wimsey's description of it as a place where "things moved in an orderly way; no one died sudden and violent deaths except aged settlers" gives it the dual in-universe/out-of-universe character of an escape from World War I and the relative modernity of city life as well as an escape from the genre of detective fiction. Wimsey with his wife Harriet returns there likewise for peace and quiet at the end of Busman's Honeymoon.
Both Peter's and Gerald's speech incorporate a dropped g, a pronunciation associated with the upper class of the time that distinguishes it from the evolving inter-war norms and helps to bolster Sayers's generally unflattering portrayal of the aristocracy (Peter excepted) as stuffy, outdated, and blustering. Gerald's outrage in Clouds of Witness that people simply did not accept his "word of honour, to say nothin' of an oath", which in his view should be sufficient to clear him of all suspicion, exemplifies this, as does Gerald's idea of the code of behaviour that precludes him from disclosing his affair with the wife of one of his tenant farmers, which would provide him with an alibi. Similarly outdated is his view that his affair with Mrs Grimethorpe is something to which he is entitled, almost as a droit du seigneur.