Immortals are beings who are immune to death through any conventional means, which is what separates them from regular mortals. This category includes the gods, the Titans, monsters, and some demigods as well. There have also been instances where a mortal or demigod has been gifted with immortality by the gods, usually as either a reward for great heroism, e.g. to Hercules, or so that they may be united in marriage with a god, such as in the cases of Psyche and Ariadne. The Hunters of Artemis are gifted with immortality so long as they keep their vow of maidenhood and do not fall in battle. Nymphs and satyrs can be considered immortal in the sense that they will never die of age. They are, however, subject to death by other means.
Immortals are immune to death in any form. They do not age, nor can they die from poison or disease. They are immune to all weapons not forged from magical metals such as Celestial Bronze, Stygian Iron, or Imperial Gold. If their bodies are somehow harmed or destroyed they will eventually reform, though the length of this process can vary from days to centuries. Almost all immortals have supernatural abilities far surpassing those of normal mortals, and they are typically hidden from human view by the Mist. However, Immortals tend to show some predictability, most tend to be very prideful, arrogant not willing to accept help from lesser beings even to the point of fading. Also Immortals tend to follow "patterns" as the Second Olympian War and the upcoming "Giant War" are just history repeating itself.
Immortality does, however, have its limits. If the body of an immortal being is damaged enough, they may be weakened into a state where they can no longer reform, even to the point of not being able to gather a complete consciousness. They can also be sealed away in prisons such as the depths of Tartarus. They can even "fade" away into nothingness, ceasing to be should they lose the will to live, which has happened to several immortal beings such as Helios, Pan, Selene,the two brothers of Briares, and the two sisters of Medusa. They also represent the state of the realm as shown by Poseidon.
Hercules was the son of Zeus. He was a great hero, for he did many brave things, like the Twelve Labors Of Hercules. The gods recognized that and he was made immortal upon his death.
Percy was also given the choice of Immortality, because he defeated the evil titan lord Kronos. Percy refused, thinking he wanted to be with Annabeth Chase. This caused a moment of confusion for the gods, since most mortals would accept the gift of being Immortal. He did, though, consider it for a moment, saying he would never age, never die, and could avoid what the Fates showed him: his whole life flashing before him until his death. In the end, he refused the gift and instead made a request to the gods to make the lives better for demigods and gods (and also peaceful Titans).
Hunters of Artemis
The Hunters of Artemis are Artemis' loyal maidens and sisters in arms. They have sworn an oath to her, vowing to remain a virgin. With this, they became immortal. They cannot die from disease or age, but if they fall in battle, they can die. Or If they break their vow to Artemis by falling in love, she does not take it lightly and stories claim she herself harms or kills the Hunter. The Hunters also gain speed, strength, and become experts at the bow and arrow, as Artemis is one of the twin archers along with her brother Apollo. Bianca di Angelo says she feels different, as if time slowed down around her, and it is the immortality. Thalia Grace claims she must join the hunt as she never felt peace since Half-Blood Hill, and she feels as if she now has a family with the Hunters. This might be because time moved slower when she was a pine tree, seemed to speed up as a human, and slowed down again when she became immortal.
While monsters can age, most monsters can't die as mortals do and will eventually come back. Whenever a monster is killed, their essence will return to Tartarus and reform, allowing them to return to the mortal world. This is true for almost all monsters, giving them some form of immortality as they can never truly die. However, the time it takes to reform can take anywhere from a few days to a few centuries to a few millenia.
There are exceptions however, as not all monsters die in the same way. Satyrs for example will be reincarnated into something in nature when they die (such as a laurel). Also, Dryads and Water Nymphs can live forever, as long as the thing their life-force is tied to isn't destroyed (plant life and bodies of water respectively). If their life force is destroyed, they will die as well.
- Main article: Fading
Fading is the only true way for most immortals to die. In the case of a god, if their realm is destroyed or not enough people believe in them, like in the case of Pan, they will fade from existence. In the case of Briares' brothers, they had faded because no one believed in them, but Percy suggested that they also stopped believing in themselves. The same can happen to monsters if not enough people remember them, but Gaea managed to find a way to reverse this somehow, as she brought back Medusa's sisters, who Medusa had claimed faded in The Lightning Thief.
- When Grover explains to Percy about what it means to be immortal in The Lightning Thief, Percy thinks it sounded like a pretty good deal. However when he was offered to become immortal in The Last Olympian, he refused in favor of another gift.