Board Thread:Lore Discussion/@comment-5632187-20130119213241/@comment-4511886-20150612101024

@Wolf of Velka

I'm fairly certain that the Hollows appeared because Gwyn relinked the First Flame, which messed up its natural cycle.

The reason why it created Hollows could be that the new power given to Light weakened the Dark, and as we know, Dark is Humanity. Without Humanity, the Undead goes Hollow.

However, I believe the "fleeting form" simply refers to Undeath, as it breaks the process of life and death. The human form is fairly predictable, it ends when the person dies. The Hollow form is also predictable, when the Humanity is depleted, the person goes Hollow for eternity. However, the Undead form is not at all predictable, some hollow in a day, others can be Undead forever. This is why I think Undeath is the fleeting form Aldia speaks of. An Undead that hasn't gone Hollow is also immortal, yet still sane, something Aldia most certainly took great interest in when conducting his experiments.

The idea that Undeath is the fleeting form is also reinforced by the fact that Hollowing, technically, happens to all creatures who lose their souls, as we can see when we fight Gwyn. He's not a human, yet he shares multiple traits with the Hollows. Namely the decaying/charred skin, inability (or lack of will) to speak and relentless aggression. Why would Aldia think the Undead are the key to life's secrets, if he was only researching Hollows, who really could be anything?