Damien Somerfield is one of the most prominent immortal charecter in the series, though he officially first appears in Book II. He is over 500 years old, but his body is frozen in time to that of a 10 year old, the age when he first obtained immortality. He reportedly acquired his immortality from a 'mystically enhanced alchemic mutagen', in other words, the Elixir of life . His immortality also grants him a powerful healing factor which allows him to recover from any wounds or injury quickly, however fatal they may be since he is immortal.
The Tiste Longa are a supernaturally infused race of winged humanoids who
serve Jrova. They are trained to be emotionless, as it it believed that emotions allow one to be easily curropted. Tiste Longa are pretty much immortal to unholy weapons,still can be killed by them, but they just come back in the Aether.With their memory of the death wiped, so they don't go seeking vengeance. they can only be completely killed by holy or demonic weapons.
Clay Wilson appeared in Book 1 and had made some appearances in Book 2. Clay Wilson was formally a sniper in the Order military before being abducted by the Order for a military experiment. Clay was injected with multiple serums that made his health regenerate alot faster than the average human, rivaling even a super. Although it made him immortal in a way, he lost half of his sanity and in rampage, killed off most of the scientists involved in the project. He managed to regain his consciousness after two hours and decided to make profit out of his immortality, becoming a freelance hero. He was hired by James Lee of Lee Enterprise to act as his bodyguard and after ther fall of ther order, and is currently serving as Councilman's Bruce Jordan's hired bodyguard during the election.