In the Highlander franchise, human beings born with the power of "the Quickening" become immortal if they suffer a premature death by unnatural means (such as by violence). After the First Death, they are ageless and invulnerable to death unless their head is removed or destroyed. From the time they are born, immortals and "pre-immortals" cannot biologically have children. Immortals can sense each other's presence and may take Quickening power from another of their kind by beheading them. They duel each other across the centuries, a deadly "Game" with few rules. One day, the last few will fight during "the Gathering" and the survivor will win the Prize, the collected energy of all immortals who ever lived, enough power to conquer or destroy humanity. "In the end, there can be only one."
These immortals are first introduced in the 1986 film Highlander, featuring Connor MacLeod (Christopher Lambert), a Scottish Highlander born in the 16th century and trained to be a warrior by an Egyptian immortal calling himself Ramírez (Sean Connery). Their mythology and nature is expanded on mostly through the live-action television show Highlander: The Series, which follows Duncan MacLeod (Adrian Paul), another immortal who belongs to the Clan MacLeod. Other films and tie-in media add their own ideas. Highlander: The Series introduced the idea that the lives and actions of immortals are recorded by a secret order of mortal humans known as the Watchers.