Progenitor

The Progenitor races - also called the Firstborn - are those that were born from the Deep as a direct result of the Deep Wells. These races gave way to all other sentient life in Wyrth, as well as a great many non-sentient species. These races are Angels, Demons, Dragons, Dreamers, Thunder Wolves, Slimes, Souls, and Strigi. While technically the actual progenitor race, Souls are not considered to be a race by most Skepsologists. Rather it is the races that possess Souls (Chimera, Dracoling, Human, etc.) that are considered the Firstborn of Animus.
One of the key features of the Progenitors is Immortality - specifically Essential Immortality. While all others possess physical forms, and thus are unaging, Souls are actually the immortal factor of their Spirit-material bond. Their mortal form will die, but the Soul will live on, eventually coming to inhabit a new form. There is no certainty they will ever be able to reawaken their sense of self, but they will not be destroyed. This is different from the other Progenitors, as they will dissipate, rejoining the Deep and reforming after a time, but fundamentally a different person - they will forget their old life - the old self effectively dying permanently. After a number of deaths, they will lose the ability to reform into their previous race entirely, fracturing into smaller pieces that become some other creature born of their cosmos. Again, the exception is Souls, as only a sundering will completely destroy them, and, when that occurs, they will never reform.
Various occurrences have altered the ways in which the Progenitors behave on a scientific or magical level, but their fundamental nature remains the same.
An example of this is the fact that Angels and Demons no longer have physical forms, instead requiring a material tether in order to inhabit the mortal world. This is not a change to their nature, but rather a factor of it. In the Age of Unity, there were only Archangels and *Demon Lords*. After an era of fighting, both had fragmented as a result of their repeated deaths, returning as lesser versions of their original selves. These lesser versions never had a physical form - they were born of the Deep after the Great Fracture - so they require a tether. The other reason they don't reincarnate as physical beings is that Holy and Dark are opposing energies. Because of this when a creature of *Celestia* kills a creature of Pandemonium (or vice versa), the Spirit is scattered. It can reform, but not as it was. The same will happen if Strigi is killed by a Dragon, or a Thunder Wolf by a Dreamer. These opposing energies destroy one another.
Another example is the fact that Dragons get generationally weaker. A truly Firstborn Dragon is a God in their own right; Aninrae is an example of this; but their children are weaker. Their children, in turn, are weaker. This is the same diminishing return that is seen in Vampires, as the Alari are the strongest, dwindling down to the following generations. In the same way, the difference is negligible in immediate generations, but very evident over longer spans. A Dragon born in the current age would be as a fly to their Age of Unity forebears. This diminishing occurs because new Dragons are not born of the essence of the old, but rather coalesced to fill the egg with life; that's why Dragons lay eggs in the first place. As a result of this, however, the elemental power cannot exceed that of the parent, causing a weaker Dragon to be born.