Mastema

Mastema (マステマ) is a fictional character in the Shaman King manga and anime series. It is a devil and a servant of Satan.

About
Mastema is the devil that terrorized Lyserg Diethel during his training in Hell. Although Lyserg's own thoughts shaped the Hell and kept him trapped there, Mastema was not created by Lyserg. Instead, it had appeared there because it matched Lyserg's hatred for Asakura Hao. Because of this similarity, by defeating the devil, Lyserg could defeat his own hatred, strengthening his soul. During this process, he also developed a combination Over Soul with Morphin and Zelel and named it after the devil: "Mastema Dolkeem".

Anime/Manga Difference
Devil Mastema does not appear in the 2001 anime series.

Trivia

 * Mastēmā (מַשְׂטֵמָה) is Hebrew for "hatred, hostility".