Rath Illuser

The Dragon Knight of Fire. One of his favorite hobbies is killing demons, and will go out of his way to seek them out. He uses the Fire Dragon sword, and later the Light Dragon Sword, as his weapon. He also boasts Ice and Fire magic and a strange ability to both create temporary copies of himself and to absorb others' powers, along with special ties to the Light Dragon. It is now known that he wasn't the true Dragon Knight of Fire. Rath harbors a great amount of self-hate, frequently projecting this hatred onto others. In volume 19, he also nearly commits suicide by Thatz Earth Dragon Sword. It takes a special person and a lot of effort to break through his many masks. He is also the only heir to the Dragon Lord. He is somehow related to the Demon Lord and believes that he shouldn't be living. Cesia and Rune are those that Rath acts naturally around. When he and Cesia travel together to look for a way to revive Crewger, Rath's demon dog, he begins to develop feelings for Cesia. He would do anything to save her from the many demons that are after her. Rath used to be an evil spirit that had possessed the dead body of the Dragon dog, Illuser. Lykouleon used his blood to turn it into one of the Dragon Tribe. After going to Nadil's castle to rescue Cesia with Rune and Thatz, Rath is captured and Cesia releases all the souls that were held inside of Rath, most notably Gil and Bierrez, and Rath disappears. It is unknown whether or not Rath is dead at this point or not and the story seems to indicate that Cesia will bring him back again at some later point. When Cesia finally revives Rath once more, he goes back to Nadil's castle where Nadil reveals that Rath is the Demon King. This finally explains Karl's inexplicable loyalty to Rath and Rath's ability to continually return to life in different bodies. (Source: Wikipedia)