Immortality (or eternal life) is the concept of living in a physical or spiritual form for an infinite or inconceivably vast length of time.
As immortality is the negation of mortality—not dying or not being subject to death—it has been a subject of fascination to mankind since at least the beginning of history. The Epic of Gilgamesh, one of the first literary works, dating back at least to the 22nd century BCE, is primarily a quest of a hero seeking to become immortal. What form an unending human life would take, or whether the soul exists and possesses immortality, has been a major point of focus of religion, as well as the subject of speculation, fantasy, and debate.
The Twilight Zone is also home to a number of immortal beings, including the Devil.