In the Harry Potter series, a Horcrux is a dark magical object created by a wizard or witch to attain immortality. This is done by splitting their soul and hiding a fragment within an object, making it difficult to kill them. The creation of a Horcrux involves committing murder, as it is the act that damages the soul. Lord Voldemort, the main antagonist, created multiple Horcruxes to secure his immortality. Each Horcrux is tied to a specific object or being, such as the Diadem of Ravenclaw or the Locket of Slytherin. Destroying all Horcruxes is essential to defeating Voldemort.