Carcer Dun is the villain of Night Watch, described by Vimes as "a stone-cold killer. With brains". He is the stereotypical psychopath, completely lacking in conscience or empathy.and is a thief and a murderer. Carcer is said to have a talent for unnerving people, an annoying laugh and a perpetual conviction of his own innocence, despite his many crimes, including at least two murders. He claims his original crime was stealing a loaf of bread (which is likely a nod to the Jean Valjean, the protagonist of Victor Hugo's novel, Les Misérables), though Vimes says that Carcer's style would be to murder the baker and steal the whole bakery. He is catapulted back in time because of an unusual combination of the weather, ambient magic, and his own inability to be civil and allow himself to be arrested. Upon arriving in the past, his first act is to mug a passing watchman, John Keel, who had just arrived in Ankh-Morpork to start a new job there. Carcer is soon arrested for being out after curfew, and wakes up in Treacle Mine Road Watch House in the next cell to Sam Vimes who was pursuing him when they were both vaulted into the past. He bribes the right people and is released. He weasels his way into the Cable Street Particulars, an evil secret police that supported the then Patrician Lord Winder, starting at the rank of Sergeant. Shortly afterwards, Carcer meets Vimes on Morphic Street which leads to a tense showdown between the Night Watch and the Particulars. They meet again after the short lived revolution on Treacle Mine Road. By this time, Carcer has been promoted to captain of the Palace Guard under Lord Snapcase. In the ensuing battle, Vimes captures Carcer, but he escapes again while they are returning to the present as a result of quantum. Once back in the present, the two meet again in Small Gods' Cemetery and he is captured by Vimes and taken to face justice and the hangman.
Carcer is depicted on the book front cover, standing to the left behind Sweeper and holding two bloodstained knives.
Carcer's name has obvious similarities to the word 'cancer' (and he is a cancer on society) but the word comes from the Latin carcerem and means jail or imprisonment (incarceration); in ancient Rome, the Carcer (pronounced Carker) was the death row cell next to the Forum. This is also the name of the villain in Charles Dicken's novel, Dombey and Son. Carcer's full name was shown in a preview of Night Watch to be Carcer Dun, but this was never revealed in the completed book. The full name would suggest that he is "done with prison" ie. never going back which is true in that he is hanged off scene at the end of the novel after Vimes captures him. His character resonates with Alex deLarge, the psychopathic protagonist in Anthony Burgess' Clockwork Orange; the incessant laughter, the malicious pranks toward his own gang members and the gratuitous evil and violence for the sake of it rather than for any monetary gain.