Subtrope of Great Detective. A sleuth who is known to belong to the higher strata of society - to have been raised in a privileged environment, and shows it, even if they have since rejected their background. Will tend to be some form of polymath, possibly autodidactic, at the least being very well-educated and well-read. Probably multilingual to boot, and often has notable eccentricities or unusual hobbies. Frequently a competent musician. Like the Great Detective, this was first instantiated in the form of Edgar Allan Poe's C. Auguste Dupin, and popularised by Arthur Conan Doyle's Sherlock Holmes.
Surprisingly few of these ever cross paths with a Gentleman Thief.
- While he's an inspector instead of a detective, Ninzaburou Shiratori from Detective Conan has the rest down to a T. He's Tall, Dark, and Handsome, comes from a rich background, is very much a Sharp-Dressed Man, and he's quite the gentleman towards women and specially to his Victorious Childhood Friend, Sumiko Kobayashi.
- Edgar Allan Poe's C. Auguste Dupin came from a wealthy family, although he had been reduced to a more humble lifestyle. Holds the rank of Chevalier (Knight) in the Légion d'honneur. Likes hieroglyphs. Can spell ratiocination.
- Arthur Conan Doyle's Sherlock Holmes is of aristocratic stock and education, but begins his story as a poor, single-minded criminologist - presumably, any family money there was would have gone to his older brother or another relative. His later fortune, social standing and range of intellectual interests are developed in the course of his detective work. It is the worldly, sociable middle-class professional Dr Watson who acts the Quintessential British Gentleman of the pair.
- Dorothy L. Sayers' Lord Peter Wimsey is another archetype. Younger brother of a duke, he was educated at Eton and Oxford, he is notably eccentric, and collects 15th Century books as a hobby.
- E.C. Bentley's Philip Trent (acknowledged by Dorothy L. Sayers as a model for Lord Peter)
- The Lady's nephew Robert in Mary Elizabeth Braddon's Lady Audley's Secret.
- Dashiell Hammett's Nick Charles, despite being possibly the most recognizable example of this, is still only a borderline example, since he grew up a working-class private eye - the son of blue-collar Greek immigrants - before marrying the heiress to a logging empire.
- Agatha Christie's Tommy Beresford, Colonel Race, and Hercule Poirot.
- Leslie Charteris's Simon Templar, a.k.a. The Saint.
- Michael Arlen's Gay Falcon.
- Randall Garrett's Lord Darcy.
- Ngaio Marsh's Roderick Alleyn.
- Margery Allingham's Albert Campion.
- S. S. Van Dine's Philo Vance
- Douglas Preston and Lincoln Child's Agent Pendergast.
- It's not clear if Nero Wolfe came from a rich family or if he's a self-made man, but otherwise he fits this trope to a tee: He's extremely wealthy, has a reputation for being a gourmet, and only leaves his house rarely and under protest—notably, once for a show involving his favorite hobby, growing orchids.
- In The Truth, William de Worde is a cross between this and Intrepid Reporter. He is estranged from his rich family though.
- Arsène Lupin is not only a Gentleman Thief, but also a detective from time to time.
- Detective Inspector Thomas "Tommy" Lynley, 8th Earl of Asherton. He is counterbalanced by his partner, the working-class Detective Sergeant Barbara Havers. She is not impressed by his wealth, title or police rank, and lets him know this at every opportunity.
- Millionaire LAPD Captain Amos Burke on Burke's Law.
- A female version appears in Dempsey and Makepeace, as DS Harry Makepeace is more properly Lady Harriet Makepeace.
- The Paul Temple detective series, broadcast on BBC radio between 1938 and 1968, features a gentleman detective who solves crimes too baffling even for Scotland Yard, assisted by his wife "Steve" and his manservant. Thought to be too anachronistic and old-fashioned when it ended in 1968, it has been periodically revived in updated one-off specials and short runs between 2006 - 2013.
- Professor Layton. The titular character is actually an archaeologist by trade, not a detective, but his "notable eccentricities or unusual hobbies" as mentioned in the intro are puzzles, meaning he gets into some mysteries. He also makes it a point to be a proper gentleman to everyone he meets.
- As noted above, C. Auguste Dupin, who appears as your partner and friend in the PC mystery game series Dark Tales.
- The Hildibrand questline of Final Fantasy XIV gives us two examples: Briardien, who plays this trope quite straight, and Hildibrand Manderville, who tries to be this (and thoroughly thinks he's successful) but is more like a chivalrous Clueless Detective.