Xellos

Xellos tends to behave like a playful trickster, answering nearly all questions directed toward him with "Sore wa himitsu desu," literally "That is a secret." He seems to delight in the frustration that ensues with his withholding of information. For the majority of the second season, Xellos acts simply for comedy's sake frequently breaking the fourth wall and addressing the viewers; all the while subtly and even sinisterly advancing the plot. Generally, Xellos' mood can be determined by the state of his eyes. If they are closed, he is acting as the "Trickster Priest," but when he opens them he brings forth the Mazoku. However, on occasion he opens his eyes out of mere surprise (as in the fourth episode of NEXT, when Lina reveals her knowledge of the Pledge Stone).

Xellos' true intentions always seem to be a mystery. As a mazoku his main goal is to return the universe into the nothingness of the Sea of Chaos, but near the end of the series he aids Lina and the others in saving the world instead. Even though he tends to manipulate Lina and the others he has saved their lives on few occasions, such as saving Martina Zoana Mel Navratilova from bandits for no apparent reason, and saving Filia during their battle with Valgaav. The reasons for doing so are never given which leads Xellos to be one of the many enigmas of the series.

Xellos is extremely loyal to Zelas Metallium and usually acts only if ordered (although at times he has aided Lina's group without having been ordered by Zelas), and it is assumed that he would gladly follow any of her requests in order to keep her pleased, even if he is not pleased with them himself (an example of this is when he was ordered to offer to kill Lina Inverse if ValGaav joined the Mazoku side in TRY).

In the novels, the Slayers group generally abhors his presence, while in the anime he is treated as more of a tolerable nuisance. In the anime, Xellos and Lina seem to have a sort of mutual respect for each other. He seems to enjoy the chaos that follows Lina, and follows her for the sake of fun even if he is not ordered to do so. In the novels Xellos seems to be more distant around her, looking somewhat troubled by the fact that Lina, unlike other humans he has dealt with, is able to see the bigger picture of things and is not tricked so easily.