Immortals are villains who cannot die and can live forever. This condition is referred to as complete immortality as opposed to biological immortality which simply means they have an infinite lifespan but can die from severe trauma.

Such villains will survive from nearly anything thrown at them or at least resurrect and/or regenerate after being destroyed. For obvious reasons these villains are among the most difficult to beat.

In many fictional universes they can still be defeated, especially if they owe their immortality to special items that if destroyed or stolen will kill them or leave them vulnerable to death. Other Divine Entities may have such powers with which to kill them.

Also, please note that ageless villains and those who are biologically immortal do not necessarily count. If the villains eventually indeed die it is often in disgrace, especially if they had to kill others and/or sell their soul in exchange to obtain it.