A Horcrux is a dark magical object in the Harry Potter series by J.K. Rowling, created through an extremely evil act: the splitting of one's soul and embedding part of it into an object. This act involves committing murder, as killing someone rips apart the soul, and through dark magic, the murderer can store a fragment of their soul in the chosen object. By doing so, the creator becomes immortal, as long as the Horcrux remains intact.