He had woken up with no recollection of who he was in a dark cave, with only an owl and a lantern to guide him. The owl seemed to be able to speak to him telepathically, and told him his name and that he had apparently been left there by his father centuries ago. By the time he'd woken up, he'd aged well and long- his hair had turned from black to white, and had grown long- though not as long as one would expect after sleeping for such a long period of time. His body had generally slowed down, and his skin was still naturally cold, matching the cave. When he tried to get out, however, there was a barrier- and so he began to delve further into the cave, with only the lantern and the telepathic owl to guide him. That is...Until he found the Staff of Eternity.
The owl had told him that the Staff of Eternity could only be whelmed my an immortal, and he picked it up with ease. This told him he was, in fact, immortal- explaining why he could live for centuries as he had, alone without food or water. He didn't want such a life, however, and was told that if he found the fountain of youth, it would correct the genetic error that kept him from dying- he'd return to a younger state, likely that of when he was left in the cave, and grow old and die like anyone else. The fountain was somewhere in that cavernous ruin...So he set out to find it, his owl companion as a guide.
