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 a police inspector instead of a private detective, Ninzaburou Shiratori from Case Closed 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.
- Benoit Blanc (Daniel Craig) in Knives Out and Glass Onion is both played straight and an Affectionate Parody, and the subject of an In-Universe New Yorker profile titled "The Last of the Gentlemen Sleuths". His exact background is unknown, though he does talk like a member of Southern aristocracy.
- Gosford Park: Inspector Thompson is a deconstruction. As part of the upper class, he immediately dismisses the house staff as suspects under the belief that none of them could have had a motive to kill the victim, a member of the landed gentry. The worlds of upstairs and downstairs are just too separate to even consider it. It's Thompson's working-class underling who knows better and solves the mystery.
- 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.
- 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.
- Nero Wolfe plays with this trope. He fits this trope to a tee on the surface: he lives a luxurious lifestyle in a classy Manhattan townhouse, 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. However, his assistant Archie Goodwin frequently notes that he needs to charge outrageously expensive fees to support his lifestyle, implying that he has no independent wealth outside of what he earns, and what hints we do get of his background suggest a life of poverty and struggle in Montenegro before finding success after emigrating to America, implying that he's closer to a Self-Made Man than an aristocrat.
- Arsène Lupin is not only a Gentleman Thief, but also a detective from time to time. Including getting nominated as the head of the French police! He was almost pitted against Sherlock Holmes (until the Doyle estate complained), so he ended up crossing paths with a Mr/ Herlock Sholmes instead.
- Ellery Queen was this is the early novels (being essentially an Expy of Philo Vance), with his late mother having been the daughter of a New York society family. However, as the series went on, his character developed and he lost most of his snobbishness (except on intellectual matters) and developed an interest in some decidedly blue collar pastimes such as boxing and baseball.
- 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.
- Roger Moore as The Saint. Moore, as Simon Templar, basically plays (with his characteristic suavity) a rich unemployed "adventurer" and amateur detective who hangs around in casinos and hotel lobbies waiting for the week's plot to arrive. In the books, Simon Templar is more of a Gentleman Thief.
- 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.