Immortality is the desired state of not dieing permanently.
The Epic of Gilgamesh is one of the earliest known instances of a quest for immortality. Gilgamesh, two-thirds god, mostly king, grows bored with boning other men's wives, and so decides to go to the Forest of Cedars, defeat the guardian monster Humbaba, and cut down the giant cedar out of pure ennui. Unfortunately, he pisses off a goddess by not sleeping with her, so his friend Enkidu dies. Gilgamesh realizes that he could die as well, and goes on another quest for immortality. Gilgamesh spends most of his life searching for immortality, but the minute he finds it (in the form of a flower), the plant gets eaten by a snake. Gilgamesh learns two valuable lessons; life is fleeting and snakes are evil.
Every goddamn time.
Recently, immortality has come under fire from the media for having the capacity to suck. 'Symptoms' of immortality include the deaths of loved ones, the universe fading out of existence, loneliness, bitterness, a feeling of inevitibility, and the realization that you are an old creepy man in a body that hasn't changed for centuries checking out innocent young girls.
The idea of immortality being a bad thing was summed up most completely by the philosopher Freddy Mercury in his thesis "Who Wants to Live Forever." Since then, popular culture has portrayed more and more of the down side of invulnerability and immortality, things that don't exist. This leaves us only to wonder what those people in positions of power are discouraging us from. Unless they know something we don't.
Immortality does occur in reality, in three different ways;