"Or perhaps in Slytherin, You'll make your real friends, Those cunning folk use any means, To achieve their ends."
Slytherin, one of the four Houses of Hogwarts School of Witchcraft and Wizardry, was founded by Salazar Slytherin at the beginning of Hogwarts in the 10th Century - or thereabouts.
He valued characteristics of cunning, resourcefulness, leadership, and ambition and instructed the Sorting Hat to only pick those students who met these. And only to pick students who were pure blood never Muggle-born. In the end, it was Salazar's feud with Gryffindor over this that caused him to leave Hogwarts.
The emblematic animal of the house is a snake, its colours are green and silver and the patron ghost of the house is the Bloody Baron.