Mr. Daniel "One Drop" Trooper is the official public executioner for Ankh-Morpork. Or, at least, one of them. In Night Watch we learn that there are two ways to hang a man - the long way (in which they are hoisted up and slowly asphyxiate) and the short way (in which they are dropped through a trapdoor and the jerk breaks the neck) and there was not a hangman in the city that would allow Carcer the easy way.
A cheerful and jovial man who is genuinely happy in his work, he is capable of hanging the condemned man to within a very inch of his life, as Albert Spangler discovered shortly after he died and met his Guardian Angel.
Mr Trooper seeks to make the experience of being hanged a short and comfortable one, and usually announces himself to clients in the condemned cells at the Tanty with "Good morning, Mr Spangler. (..) It’s me, sir, Daniel “One Drop” Trooper. I am your executioner for today, sir. Don’t you worry, sir. I’ve hanged dozens of people. We’ll soon have you out of here".
He's also a bit of a thinker. 'Do you really think all this deters crime, Mr Trooper?' Albert Spangler asks him. 'Well, in the generality of things I'd say it's hard to tell, given that it's hard to find evidence of crimes not committed,' said the hangman, giving the trapdoor a final rattle. 'But in the specificality, sir, I'd say it's very efficacious.' 'Meaning what?' said Albert. 'Meaning I've never seen someone up here more'n once, sir. Shall we go?'
He has a profitable pension plan in the form of holding the concession to sell memorabilia of public hangings, and owns a special pen capable of writing on rope. The condemned person is usually politely invited to sign the noose at two-inch intervals as a contribution towards Mr Trooper's pension plan. Vetinari no doubt nods at the expense of a new rope for each hanging, as Mr. Trooper's expertise, which is second to no man's, has proven of great and valuable worth to him on at least three occasions that readers of the books know about.
Mr. Trooper is an avid reader of What Gallows and the Tanty Bugle, partly for professional reasons and mainly for the financial information in the "used rope" pages. Apparently, the Sto Plains Dealer and the Pseudopolis Herald are also good for trade-related financial information.
Mr. Trooper appreciates the showmanship aspects of his trade, and is always appreciative of light banter with the condemned person, ideally culminating in a memorable bon mot just before he pulls the lever.
A previous post-holder of the job of Civic Hangman and Public Executioner was Hepzibah Whitlow, who also had a reflective and thoughtful approach to the job. At some point before Mr Whitlow, the father of the witch Mrs Proust held the office of Civic Hangman. It is not known what her maiden name was but if she adhered to the witch custom where family names are passed down through the female line (refer to the Oggs), then her father would have been Mr Proust too.
Whether or not Mr. Trooper is based on a real figure is unknown. It is tempting to think Pratchett had the Canadian rock band Trooper in mind since one of their hits was "Raise a little Hell" a place where many of "One Drop Trooper's" clientele go shortly after their time with him. This connection is unlikely however.