The Hogwarts founders, alternatively known as the Hogwarts Four, were four wizards and witches who established Hogwarts School of Witchcraft and Wizardry during the High Middle Ages of the 10th century. These four founders are widely described (mostly by the British) as being the most brilliant witches and wizards of the time and were the following: Godric Gryffindor, Helga Hufflepuff, Rowena Ravenclaw and Salazar Slytherin. Each of them created their own House, named after themselves via their surname; Gryffindor, Hufflepuff, Ravenclaw and Slytherin respectively, and laid the foundations for one of the most prestigious Wizarding school in the magical world.
The founder of Gryffindor house. Godric was a fair and noble Englishman, albeit accused of unprofessionalism, arrogance and bias by Slytherin. A testament to his history as a Knight, Godric valued courage and bravery above all else and instructed the Sorting Hat to pick his students accordingly. Gryffindor's heirloom is the Goblin-made Sword of Gryffindor, forged for him by the King of the Goblins himself. It was charmed to present itself to any true Gryffindor in a moment of need. Godric's relationship with Rowena Ravenclaw was undoubtedly the closest, with the two becoming husband and wife sometime after Hogwarts was founded. He maintained a good friendship with Helga Hufflepuff but had a tough rivalry with Salazar Slytherin. They were once close friends, but Gryffindor's behaviour towards Slytherin and their disagreements on how Hogwarts should be run led to them breaking apart their friendship.
The founder of Hufflepuff house, Helga Hufflepuff was a kind-hearted and warm Welsh woman who mostly valued people above the traits within them. She believed that anybody could be shaped into a good person and famously said that she would "take the rest;" she believed that she could shape anybody into a person who was loyal, patient and hard working. Helga was the one who brought the house-elves to Hogwarts in order to help them maintain the castle and serve the children during the school's growth. She maintained a good relationship with the rest of the founders and was the lover of Salazar Slytherin, with whom she conceived a child just before he left Hogwarts. Helga was the final founder to remain as their Head of House; Salazar had left Hogwarts, Rowena had died of an illness and Godric had disappeared searching for Slytherin. On her deathbed, Helga handpicked the first Headmaster of Hogwarts before passing away peacefully. Hufflepuff's heirloom is her famous cup, which was passed down through her brother's family until finally being returned to Hogwarts in the 90's.
The founder of Ravenclaw house. Rowena Ravenclaw was an amazingly intelligent Scottish woman with a sharp tongue. Intellect was a highly valued asset to Ravenclaw and made it one of the key traits in which to pick her students. Prior to the establishment of Hogwarts, Rowena had a daughter, Helena, who would later become the Grey Lady of Hogwarts. Helena had stolen her mother's diadem and it became lost somewhere in mainland Europe. It was only returned to Hogwarts after Lord Voldemort, who had found the diadem with Helena's help, was defeated at the Battle of Hogwarts. Rowena was the wife of Godric Gryffindor and the best friend of Helga Hufflepuff. She also maintained a good friendship with Salazar Slytherin in their early years due to him being able to challenger her intelligence, but when his friendship with Godric broke down, she took her husband's side and pushed him away.
The founder of Slytherin house. Salazar Slytherin was a pure-blood Irish wizard who was sly and cunning who prided himself on being able to "think outside the box." Slytherin fostered a hatred for Muggle in his early years because his sister and niece were killed in a Muggle witch hunt, but that hatred seldom boiled over to Muggle-born students and Slytherin's attitude towards them softened over the years. He created the Chamber of Secrets as a way to secretly teach students the Dark Arts; the room housed a Basilisk, which was bred to protect the students in the event of an attack on the school. Slytherin was the lover of Helga Hufflepuff, with whom he would unknowingly conceived a child with prior to his departure. The identity and fate of this child is lost to history. Slytherin left Hogwarts after a fiery argument with the other founders and wouldn't return for decades. Godric Gryffindor sought him out and challenged him to a duel, which Salazar won. He was the longest-lived founder, dying after all three founders, and entombed himself in his Chamber of Secrets, clutching his locket and dying peacefully at the age of 91. Salazar's fate remained a mystery until the opening of the Chamber of Secrets by Harry Potter and his friends in 1993.