Janos Slynt was former Lord Commander of the the City Watch, also known as the Gold Cloaks. It has long been known that Slynt is making money by taking a part of each gold cloaks salary. Stannis wanted him prosecuted, but witnesses were murdered. Littlefinger interceded with King Robert (apparently the crown was getting a cut of this as well. Janos betrays Eddard Stark to the Lannisters and is rewarded by being made Lord of Harrenhal.
In the booksEdit
Eddard Stark was named regent by King Robert in a proclamation (until his heir comes of age). Lord Eddard tried to stop Cersei Lannister from seizing power at the death of Robert Baratheon. He believes that Petyr Baelish has arranged for the Gold cloaks to support him, allowing him to hold the throne for Stannis Baratheon (who he knows is the rightful heir). Littlefinger betrayed Eddard, the Gold Cloaks working with the Lannister men kill all of the Stark household, except steward's daughter, Jeyne Poole. As a reward he is given the high lordship of Harrenhal by Cersei Lannister. Cersei also orders Slynt to have the Gold cloaks kill all of Robert Baratheon's bastard children. Partly because people looking at them can perceive that her own children are not Robert's heirs, but also to get back at Robert. Janos Slynt sends a nasty gold cloak named Allar Deem to kill baby Barra. When Tyrion Lannister comes to King's landing as acting Hand of the King. He has Janos sent to the wall. He wants to break Cersei's power (Janos is beholden to her), but also Janos is corrupt (he was bought by Cersei through Littlefinger) and he is morally bankrupt (as he ordered the killing of a baby).
Janos is not seen again until book three, where at the death of Jeor Mormont, Slynt is one of the candidates up for election to take leadership of the Night's Watch. He is building support and seems destined to win. Samwell Tarly is very anxious that this not occur, as Slynt expressed the wish to punish Jon Snow for desertion and murder. Sam first tries to get the other candidates to vote for each other, that failing he succeeds in getting them to compromise on another candidate, Jon Snow. Janos Slynt is enraged.
Janos Slynt continues to question and flaunt Jon's authority. Finally going to the point of refusing to obey an order. Jon orders him to take a group of Night Watch men and wildlings to one of the abandoned castles at the Wall to restore and open it. Jon gives him the night to reconsider his refusal. The next day, he is going to have Slynt imprisoned, but realizes that Janos will always make trouble and must be an example. Jon Snow having ordered Slynt's execution, follows the example of his father Eddard and beheads Lord Janos himself using Longclaw.