Slytherin was home-educated in magic by his parents and became well-versed in the Dark Arts. At a young age, a Viking raid on Slytherin's village killed his parents, forcing Salazar to raise his sister on his own while only a teenager. When Salazar was twenty-four, Elianna and her newborn child were murdered by Muggles, which made him foster a hatred for them. Salazar found himself in eastern England, where he became enamoured with snakes, doing experiments on them to try and make them talk. One day, he met Godric Gryffindor, an English knight and powerful wizard. Together, along with Rowena Ravenclaw and later, Helga Hufflepuff, created Hogwarts. He headed house Slytherin and along with the other founders, chose his students himself. Salazar was often at odds with Godric Gryffindor due to Godric's perceived unprofessionalism and arrogance. Salazar created the Chamber of Secrets as a way of secretly teaching a select-few Slytherins the Dark Arts, as well as housing a Basilisk, which would be used in the event of an attack at Hogwarts to defend the castle and the children. While teaching at Hogwarts, Salazar and Helga Hufflepuff fell in love, however Salazar's rivalry with Godric Gryffindor brought stress upon their relationship. With Rowena Ravenclaw siding with Godric, her husband, Salazar made the decision to leave. He asked Helga to and leave with him and get married, but she refused, stating that she still owed too much to the school and could not bring herself to abandon it. Unbeknownst to him, he sired a child from his romance with Helga.
Salazar left the grounds of Hogwarts heartbroken and angry. He would never see Helga again, but in his final days, was visited by Godric Gryffindor, who challenged him to a duel. Salazar killed Gryffindor, and buried his body in an unknown location. Godric's sword returned to Hogwarts without its master, indicating his demise. Salazar returned to Hogwarts in 1026 only to find Helga Hufflepuff had passed away three years prior. After a visit to Helga's grave, Salazar entered the Chamber of Secrets for the last time and peacefully died in the underground mausoleum, clutching a photo of him and Helga together. Unfortunately, after Salazar's departure, his reputation was tarnished by Godric, who insisted Salazar was an evil wizard and a pure-blood supremacist who wanted to rid the school of all Muggle-borns, when in reality Salazar's hatred of Muggles softened over the years and never boiled over towards Muggle-born students. Salazar was the last of the founders to pass away, though his fate wouldn't be known until the opening of the Chamber of Secrets by Harry Potter nearly a millennium later.