Mephistopheles

Mephistopheles was a demon from YGGDRASIL.

Personality
Mephistopheles was atypical from regular demons as he strove to be good and was known to be a helpful NPC that assisted players.

Background
Mephistopheles was a character who was famous for spouting tsundere lines to good-aligned beings. He looked fearsome, but was surprisingly friendly and logical. Also, he gave out missions that ranged from rewarding to high-level, which made him almost as popular as the Dark Young.

The Craftsman of Dwarf Arc
Gondo Firebeard exclaimed his disbelief that Ainz Ooal Gown was a friendly undead, as such a thing was unthinkable. Ainz countered that he heard of more bizarre creatures going against their alignments such as a angel falling to darkness and Mephistopheles, a demon, striving to the light.

Trivia

 * Mephistopheles is named after a demon from German folklore that advises the scholar Faust from selling his soul to the Devil.