The Hogwarts founders, also known as the Hogwarts Four, were four witches and wizards who established Hogwarts School of Witchcraft and Wizardry during the medieval era, in the 10th century. These four founders are widely described 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: Gryffindor, Hufflepuff, Ravenclaw and Slytherin respectively. They laid the foundations for the largest and most prestigious Wizarding school in Britain.
The founder of Gryffindor house. A fair man, he believed that any child who displayed magical abilities before their 11th birthday should be able to attend Hogwarts. Godric valued courage and bravery, believing these were the two most virtuous abilities a person can possess. Gryffindor was the original owner of the Sorting Hat, which he and his fellow founders enchanted to select people to be sorted into their houses, by seeing the qualities each founder valued the most.
Gryffindor also had a sword made, which would present itself to any true Gryffindor in a moment of need. The sword became an important item a thousand years later, and was instrumental in defending Hogwarts from Slytherin's descendant. He was allegedly the best friend of Slytherin before he left Hogwarts. His house corresponds to the element of fire.
The founder of Hufflepuff house. A kind and warm woman, she valued a person must possess to be sorted into Hufflepuff house are those of loyalty, patience, and hard working above all else. It is also known that she brought the house-elves to Hogwarts. She owned a fine golden cup which was fairly innocuous aside from being her possession. The cup was sought by Lord Voldemort nearly a thousand years later, for him to turn it into a Horcrux. She was the best friend of Rowena Ravenclaw. Her house corresponds to the element of earth.
The founder of Ravenclaw house. A sharp and intelligent woman, Intellect is a highly valued asset to the students of Ravenclaw house. Due to this, it is likely that Rowena wanted to make Hogwarts the very finest Wizarding school on earth, teaching those children with the highest intelligence. Rowena also had a daughter, Helena, who later became the Grey Lady of Hogwarts as a ghost.
Helena stole her mother's diadem, and it became lost. It was believed to have been lost for so long, that no one alive had seen it, however, it had actually been found by Lord Voldemort with the aid of the ghost of Ravenclaw's daughter. He turned it into a Horcrux and later hidden once more, this time within the Room of Requirement, where it would remain hidden for at least 50 years. She was the best friend of Helga Hufflepuff. Her house corresponds to the element of air.
The founder of Slytherin house. Sly and cunning, he was not unlike many of the students he brought into his house. He believed strongly that only wizards of pure blood (i.e., those with a mother and father from wizarding families) should be allowed to attend Hogwarts. Slytherin caused great dispute over this with the other founders, and it eventually caused a permanent rift with Gryffindor, which led to Slytherin's departure from the school. Before he left, however, he created the Chamber of Secrets, complete with a huge statue of himself and a horrible monster.
Almost a thousand years later, Slytherin's descendant, Lord Voldemort, would seek to fulfil his desires of banishing Muggle-borns from Hogwarts, and exterminating them. One of his personal effects, a locket, was later claimed by Voldemort, to be used as a Horcrux. He was the best friend of Godric Gryffindor before the rift occurred and he left Hogwarts. His house corresponds to the element of water.
After the founding of Hogwarts school
After Hogwarts was built, the founders co-existed peacefully for many years. Eventually, however, the pressure from Slytherin to admit only pure-blood wizards affected the other three founders greatly, and none more than Gryffindor. Slytherin finally left Hogwarts following a massive argument with Gryffindor over the issue, and he never returned.
Link to Lord Voldemort
Each of the founders would later be linked to the Dark Lord, Voldemort, in some way, as he used an item belonging to three of them for several of his Horcurxes.
Slytherin himself was the Ancestor of Voldemort. Voldemort aspired to see his vision of a pure-blood only Hogwarts come to fruition, as well as ridding the rest of the world of muggles. Slytherin's Locket was one of Voldemort's Horcruxes.
Ravenclaw's Diadem was sought by Voldemort to be one of his Hocruxes. Voldemort found the missing Diadem by asking for it's location from Ravenclaw's daughter, Helena, and promised that he would destroy it, however he broke his promise as soon as he had it.
Hufflepuff's Cup was claimed by Voldemort from Hepzibah Smith, a collector of antiquities, who also had the Locket of Salazar Slytherin. The Cup was entrusted to Bellatrix Lestrange for safe keeping.
Voldemort didn't acquire an item from Gryffindor, although it is believed by some that he may have intended to use the Sword of Gryffindor. Although it wouldn't present itself to him since he was not a true Gryffindor, the sword would later become key to Voldemort's defeat, as it was used to kill Salazar Slytherin's Basilisk, when Voldemort tried to rid Hogwarts of Muggleborns by reopening the Chamber of Secrets, which resulted in it being infused with the venom of the Basilisk, granting it the ability to destroy Horcruxes, being used to destroy three of them.
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