Thanatos is an evil shape-shifting monster. In its regular form, it appears as a snake-like creature with arms and legs covered in some sort of black cloak.
The Thanatos is a monster that feeds off of death, pain, and fear. It formerly lived in the small country of Kryo, were it killed many people in order to gain more power. It has been noted to be the murderer behind the death of Lysander's mother and father, as well as many other innocent people.
The people of Kryo lived in fear of the Thanatos for many years, until one day it seemed to vanish. When Lysander tried to fight the monster in order to get revenge, the Thanatos was never seen again. The country celebrated the monster's disappearance, though Prof. Loukianos Ilios, a teacher and headmaster of the Kryo Academy of Education, began to doubt if this was truly the correct time to celebrate. He thinks that Lysander did not drive off and/or kill the monster like it had seemed, but instead the monster now resides inside the boy himself, which would explain his sudden skill in dark magic right after the encounter.
The Thanatos can turn a human or animal into one of it's followers, or "Wraiths", by draining all of the energy inside the human or animal. Though, it rarely ever does this, and most wraiths are caused by a human giving up his or her humanity to become a more powerful follower of the monster.