Xellos (ゼロス Zerosu?) (sometimes spelled Xelloss) is a fictional character and primary figure in the Slayers fantasy Manga, light novels, and anime. He is a powerful Mazoku (demon), who is both a help and a hindrance to protagonist Lina Inverse and her friends.

Xellos is the single most powerful servant of Zelas Metallium, who in turn is one of the five retainers of Ruby Eye Shabranigdo, one of the Slayers series' deity-like beings. Because of this relationship, some consider Xellos Metallium to be his full name, but he calls himself simply Xellos, the Priest.[1]