The Alpha Vampire - an example of an immortal being.
Immortality is the ability to live forever, and not being subjected to aging or disease.
Known Holders
Near-Absolute Immortals
These particular beings are considered to be constant, nearly completely indestructible and immune to age and disease, although they are not completely indestructible and can still be banished or killed.
- Dean (formerly) - As a Knight of Hell and with the Mark of Cain, he is virtually immortal. Unless he transfers the mark to someone else, and is killed by The First Blade, Dean will never die neither by natural or supernatural means. It is highly implied that he cannot kill himself with the blade, as it had no effect on him when he slit open his hand.
- Cain - As he bore the Mark of Cain, he could not be killed by anything with the exception of the First Blade.
- Lucifer (formerly) - As a former bearer of the Mark of Cain, Lucifer was nigh-indestructible.
- The Shadow - An entity that holds near absolute power within the Empty, a place predating God and the Darkness. Not much else is known about it.
- Death - Death was nearly invincible and couldn't be killed except by his scythe.
- God - Death claimed that he could kill him, but he died before this could be tested out. His older sister, The Darkness, has the power to kill him.
- The Darkness - A primeval yet destructive force that has existed alongside God, only her brother is able to kill her, with the help of the Archangels.
Advanced Immortals
These particular beings are immune to age, viruses, and disease. However, they can still be killed through the use of special weapons, powers and rituals and more powerful beings.
- Archangels - Archangels have an infinitely long lifespan and aren't subject to time, even their vessels are unaffected by age or diseases, they also don't need to breathe, eat, or sleep to sustain themselves. They are some of the oldest beings in all of Creation. They're nearly indestructible, but souls and an Archangel blade can hurt and kill them, as can God, Death, Amara and Jack.
- Eve - Eve is immortal and cannot die of disease or old age. She was older than even the angels.
- Leviathans - Being creatures older than humans, souls and angels. Leviathans are immortal, in a variety of senses, having an ageless lifespan, meaning they simply do not age. Leviathans cannot be killed unless by two means, one of which - a weapon - was devised by God. The other way for them to die is for them to be eaten by another Leviathan, or for the Leviathan to eat itself.
Higher Immortals
- Angels - Angels, even in their vessels, do not age and cannot be killed by diseases, toxins or Earthly weapons.
- Demons - Demons do not age and cannot be killed by conventional means.
Other Immortals
- Alphas - As the first of their species, they have been around for a very long time without apparently aging. They can potentially live forever.
- Crocotta - They have a longer life span than humans, able to live for centuries.
- Deities - Pagan deities can live forever as they are immune to aging and disease. Many have been around for centuries or even millennia. Each one has a unique way to be killed.
- Djinns - Djinns can possibly live forever or at least live several hundred years.
- Doc Benton - His method of immortality had nothing to do with magic, spells or rituals are not a part of the formula, only science which was apparently of his own creation. It's stated by Doc Benton that there is a formula, suggesting that it was a chemical. He did however, steal other people's organs and body parts to replace his own when they ran down, or got damaged, this is most likely out of convenience though, as he can still act normally, when they are damaged beyond repair. He was also able to give others the formula, and thus his powers.
- Golem - As a non-biological being, it doesn't age or die by conventional methods.
- Horsemen - Powerful and nigh-indestructible entities.
- Nachzehrer - Nachzehrer do not age and cannot be killed unless they are beheaded with a copper coin in their mouths.
- Kohonta - A kohonta has the capability to live for centuries.
- Phoenix - Phoenix are immortal and they do not age at all. A Phoenix is immune to death by natural causes and aging. Based on Elias's comments, it seems before the Colt, there was no known way to kill a Phoenix, although the fact it was known that they combust upon death, implies there are other ways to kill them, though that could have been a paradox.
- Luther Shrike - Granted immortality inside of his property by Barthamus after blackmailing Barthamus with his human bones. Could be injured but not killed inside of his property as a result. Outside of his property, Luther was vulnerable to being killed.
- Shtriga - By feeding off life force, the Shtriga can live for an extended period of time.
- Vampires - Vampires can potentially live forever. They can not grow old and aren't affected by conventional diseases that affect humans.
- Wendigo - Wendigos can live forever, supposedly about hundreds of years.
- Kappa - Kappas can live over 100 years old.
Simple Immortals
These are beings who could live forever and are immune to age and disease, however they can die as easily as mortals from physical wounds.
- Clive Dylan
- Eleanor Visyak
- Inyo
- Lily Sunder
- Oskar
- Randa Moreno
- Witches
- Don Harding
- Don Stark (presumably)
- Lia
- Maggie Stark (presumably)
- Patrick
- Rowena MacLeod
- Tracy Davis
- Charlie
- Methuselah
Trivia
- It is unknown what can actually injure and/or kill a Cambion (a human-demon hybrid). It is also unknown whether they can live forever or whether they grow old similarly to normal humans. However, Castiel attempted to use the Demon-Killing Knife to kill Jesse, a Cambion, so it can be presumed that at the very least at Castiel's opinion/belief, it can kill him (albeit, the actual effectiveness was never shown).