Mephistopheles

"'Mephistopheles used to be the leader of the RAD Newspaper Club, but got demoted by Lucifer after creating the Prince Lucifer and Princess Diavolo stickers. He doesn't like how Diavolo gets chummy with ex-angel Lucifer.'"

Mephistopheles is a demon and student of RAD that made his first appearance in Lesson 63-1, though he was mentioned much earlier in the Daily Chat titled The Popularity Contest. Little is currently known about him, though he initially seems to have an unfavorable opinion of MC.

Story
Note: this section may include spoilers

In the first-ever RAD Newspaper Club chat, Mephistopheles was in 10th place in the unofficial results of a popularity contest, but he and Mammon were disqualified due to falsified ballots. This was later commented on by Asmodeus, Satan, and Leviathan, with the latter being upset he only made the list after the disqualifications. Together with Satan, Asmodeus, and Mammon, he designed the chat stickers Prince Lucifer and Princess Diavolo.