Xellos

Xellos the Mysterious Priest is a character from the Slayers series. As the name implies, his origins remained a mystery, thus making the Fantasy Adventure Team uncertain if he's on the good side or on the bad side.

His catchphrase when questioned about any sort of knowledge is "that is a secret!".

Trivia

 * Xellos debuts on Benny, Leo, Johnny and Rae Meet the Great Beast.