Inspector Alleyn is the very essence of the gentleman detective. First of all, he's of fine breeding. Consider the fact that he went to Eton, and his brother is called Sir George Alleyn. That should give you some idea of how blue his blood is, as will the way he speaks. Alleyn has the clipped, immaculate English accent of a mid-20th Century BBC announcer, and you just know he has an unfaltering command of grammar as well. (And let's not ignore the fact that his first name is Roderick, for heaven's sake.)
Existing in a realm of exclusive London clubs, stately homes and government offices - he has a shady sideline in espionage - Inspector Alleyn exudes the sort of sophistication you just don't see much of nowadays. In fact, just watching him work for a few minutes will make you feel nostalgic for an era you're probably too young to even remember. Ahhh.
Who is Albert Campion? We honestly don't know. Rather like a superhero, he has taken on an alter-ego: Campion isn't his real name. All we can tell is that he's a man who comes from money, has a taste for natty suits, and has the means and inclination to spend his days sauntering around, casually solving crimes. In that sense, he's even more of a "gentleman detective" than Alleyn, because it's not even a job he gets paid for. He just does it because he can, as if it's a pleasant hobby.
Other reasons why he's a perfect gentleman detective: he wears delicate spectacles that make him look all innocent and unassuming, he goes around in a rather splendid car, and he has an actual, honest-to-goodness manservant. Now that's something even Inspector Alleyn doesn't have, and proves just how upper-crust Campion is. Good thing he's doing something worthwhile with his cash, really.
Ah, Lynley. The very lyrical sound of his name makes one think of bone-china tea cups, floppy hair, and English country gardens. And he certainly lives up to it all. Thomas Lynley is more than just a little bit posh - he's a full-on royal. The 8th Earl of Asherton, if you please. The very first time we see him on screen, he's attending a society wedding in a rolling country pile, and that's pretty much an average day in the life for this dashing detective.
With his taste for horses and glossy-haired English rose ladies, Lynley should really be off being a modern-day Bertie Wooster somewhere. Yet, being a noble sort, he chooses to spend his days as a police inspector, mingling with coppers who view him as an aloof aristocrat. And that includes his own partner, Havers. Doesn't put him off, though, and he's never anything less that courteous and gallant towards everyone he meets. Capital chap.
He's not the richest detective on this list, but Adam Dalgliesh may well be the most cerebral. And that's saying something, when you remember that all gentleman detectives are renowned for being on the brainy side. Dalgliesh has the sharp, inquisitive mind you'd expect from a top sleuth, but it's married with a certain artistic sensibility. A wistful, romantic, creative soulfulness that really sets him apart from the gruff coppers he works alongside.
Gentle and genteel, Dalgliesh is the sort of fellow who spends his evenings pondering things and writing poetry. Even his choice of love interests reflects his sensitive and academic nature - one of them is a Cambridge literature professor. Short of going out with a duchess, we can't think of a better match for a true gentleman detective.