What We're Permitted To Know
Xellos appears in NEXT and TRY, the second and third series' of Slayers. He also briefly makes an appearance in Slayers Premium. He first appeared to Lina and her companions after Lina's savage behaviour to a bandit gang in a town, searching for the Clare Bible. Xellos presented him as "Xellos, mysterious priest" and had them instantly doubting his character, especially after he admitted to lying immediately after giving them an explanation of why he was after the Clare Bible. From then on Xellos watched close by as Lina and co got into all sorts of mischief.
It wasn't until the journey in the desert room with the Clare Bible tablets was Xellos exposed by Gaav as a high level Mazoku. Even still, Xellos allowed himself to be wounded by Gaav. Upon escaping, Xellos and the group headed for the Kakato Mountains on advice by Auntie Aqua. There, in the mountains where Dragons reside, the Dragon Milgasia looked upon Xellos with fear, as Xellos had killed thousands of his people within seconds a millennium before in the War of the Monster's Fall. It was at this point in the show where the full view of Xellos came into perspective. His friendly smiles and charming welcomes were nothing more than the mask of an evil, bloodthirsty demon. To say Xellos has a good and evil side would be false, as his intent is always to serve his race, using whatever means necessary to achieve his goal.
Xellos is cautious around the Clare Bible Being a Mazoku you'd expect he'd try to steal it, but he is no fool and knows his place, it a power far greater than his and in a dimension he could easily be lost in for eternity.
After battling Gaav again, Xellos disappears for some time, reappearing to return Gourry's sword. Note, this was not because he wanted to be a good friend, but because Gourry having the sword at the immediate time was to his advantage. Now they thought that was the last they'd see of Xellos...how wrong they were.
His first face to face with the Golden Dragon wasn't pleasant to say the least. Filia, angered by his presence began what would be a on-going trend of taunts and especially the use of the word "Namagomi" meaning "raw garbage". As Filia runs from him, he makes a face, clearly angered by her comments. Xellos losing his composure had never ocurred before this.
Xellos's first mission was the destruction of Valgaav, until new orders to offer Valgaav a chance to join the Mazoku. Upon refusal, he was kill him. Xellos did as such and delighting in beating him, surprised when Valgaav fought back and wounded him. It was Filia who came to his aid and attempted to help him to safety. After Darkstar's near release, Xellos stuck around with Almace and his two people, waiting for Lina to do their work for them. Xellos entered the scene as soon as the temple in the North had been opened. He threatened the Elder Golden Dragon with Filia's life if he did not open the barrier to the last weapon. The Elder could not, and was willing to sacrafice her life for the greater good anyway. Did Xellos miscalculate her worth based on what he thought of her? Xellos didn't kill Filia, he let her go. Suspicious considering he has gladly killed thousands of her kind - and we all know a Mazoku like Xellos doesn't need to make empty threats.
Xellos eventually helps to bring together all the Darkstar weapons, weilding the bow, the last weapon, until the final battle. In the end he and Filia were the light and darkness of the prophecy, joining together for the greater "good" of their world. After everyone went their separate ways, Xellos returned to Wolfpack Island to give his report.
Secrets Revealed
Xellos is a Mazoku, meaning "Evil Race". He is a demon, and in the english dub a "Monster". He is the only General and Priest of Xellas/Zelas Metallium, one of the four Dark Lords created by Shabranigno. The true form of Xellos has been in question for some time, some say he was once human, others that he is a Black Cone. According to MAGIUS Slayers RPG book 1 and Secrets of Slayers, Zelas raised her lover and gave him both the abilities her Head Priest, as well as General. The SoS book's knowledge is under question though.
Xellos's master resides on Wolfpack Island and is said to have a Human, Wolf and Mazoku form, and surrounds herself with wolves and other creatures. Zelas is also a heavy drinker, as well as a chain smoker. It also believed she treats Xellos as her son, this coming from her being the only Lord to give herself a last name. Xellos offcially doesn't have the last name Metallium, however if the information of Zelas treating him as a son is true, then it is logical he would.
Can Mazoku Love?
The age old question. I believe so. Mazoku are sentient creatures after all, with as much a wide range of emotions and feelings as any other freeling thinking creature. Xellos displays he feels joy, and what Mazoku wouldn't around such twisted and tasty energy found from the Slayers cast. Emotion such as love, especially romantic love, can be felt, however incredibly painful physically if not controled.
