the idea of the Slytherin King was originally given to me by the author Mad Martha. The current history in this fiction is my own, and only the basic premise of this particular political process remains
House Politics
There is a very delicate system of power within the houses at Hogwarts school of Witchcraft and Wizardry. One house in particular stands out among these micropolitical systems and it is, as one would have guessed, Slytherin. Slytherin is the house of the serpent, some even descendants of Salazaar Slytherin himself. The most famous dark wizards of the past several centuries are rumored to have been bred inside this system with great care, and an even greater title. The King of Slytherin.
Slytherin Kings are, as is implied, the leaders of the Slytherin House for a year. Now, there is no election, per se, to determine the King for each school year. Usually males from the eldest and most powerful, most wealthy, and most devious families assume position at the start of each year. The King is usually a seventh year, and therefore each King names the King to succeed him.
In 1991, Lee Nobles had been the frontrunner in his sixth year, but upon hearing that Lucius Malfoy's first born son would be in attendance of Hogwarts instead of Durmstrang (and knowing Lucius' standing with the Dark Lord) he quickly stepped down. On the last day of the term he announced that this spot were to be reserved for Draco Malfoy. There were gasps from the entire common room. It was very rare for anyone who wasn't a seventh year to inherit the title of the Slytherin King; and it was even rarer for a first year (in fact, this was the first time, to anyone's knowledge, that it had ever happened).
There is, however, a way in which a frontrunner that was not named the newest monarch can take the crown: a duel. Although this hasn't been the case in quite some time (not since Tom Riddle's time, in fact) there was a gleam in Lee Nobles' (and several others) eyes even as he announced his decision to concede.